feat(ui): Phase B — sidebar drawer + SystemStatusDot + 키보드 nav

- +layout.svelte: 햄버거 → IconButton, 우측 nav → Button ghost,
  sidebar overlay → Drawer (uiState 단일 slot),
  Esc 글로벌 핸들러 ui.handleEscape() 위임 (5대 원칙 #2)
- lib/stores/system.ts (신규): dashboardSummary writable + 60s 폴링,
  단일 fetch를 SystemStatusDot(B)와 dashboard(C)가 공유
- SystemStatusDot.svelte (신규): 8px 도트 + tooltip,
  failed > 0 → error / pending > 10 → warning / 그 외 → success
- Sidebar.svelte: 트리에 ArrowUp/Down 키보드 nav,
  활성 도메인 row에 aria-current="page"

frontend/src/lib/components/Sidebar.svelte

@@ -66,6 +66,24 @@
   });
 
   let totalCount = $derived(tree.reduce((sum, n) => sum + n.count, 0));
+
+  // ArrowUp/Down 키보드 nav — 현재 펼쳐진 tree-row만 traverse
+  function handleTreeKeydown(e) {
+    if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp') return;
+    const root = e.currentTarget;
+    const rows = Array.from(root.querySelectorAll('[data-tree-row]'));
+    if (rows.length === 0) return;
+    const active = document.activeElement;
+    const idx = active ? rows.indexOf(active) : -1;
+    let next;
+    if (e.key === 'ArrowDown') {
+      next = idx < 0 ? 0 : Math.min(idx + 1, rows.length - 1);
+    } else {
+      next = idx <= 0 ? 0 : idx - 1;
+    }
+    e.preventDefault();
+    rows[next].focus();
+  }
 </script>
 
 <aside class="h-full flex flex-col bg-sidebar border-r border-default overflow-y-auto">
@@ -91,7 +109,7 @@
   </div>
 
   <!-- 트리 -->
-  <nav class="flex-1 px-2 py-2">
+  <nav class="flex-1 px-2 py-2" onkeydown={handleTreeKeydown}>
     {#if loading}
       {#each Array(5) as _}
         <div class="h-8 bg-surface rounded-md animate-pulse mx-1 mb-1"></div>
@@ -123,6 +141,8 @@
 
             <button
               onclick={() => navigate(n.path)}
+              data-tree-row
+              aria-current={isActive ? 'page' : undefined}
               class="flex-1 flex items-center justify-between px-2 py-1.5 rounded-md text-sm transition-colors
                 {isActive ? 'bg-accent/15 text-accent' : isParent ? 'text-text' : 'text-dim hover:bg-surface hover:text-text'}"
             >

frontend/src/lib/components/SystemStatusDot.svelte

@@ -0,0 +1,89 @@
+<script lang="ts">
+  // 시스템 상태 도트 — Phase B 신규.
+  // dashboardSummary store를 구독해 한 색상 + tooltip을 표시한다.
+  // 색상 규칙(우선순위 순):
+  //   1) failed_count > 0           → bg-error
+  //   2) 어떤 stage라도 pending > 10 → bg-warning
+  //   3) 그 외 (failed_count === 0) → bg-success
+  // 첫 fetch 전(null)에는 dim 회색 표시.
+
+  import {
+    dashboardSummary,
+    type DashboardSummary,
+    type PipelineStatus,
+  } from '$lib/stores/system';
+
+  type Tone = 'success' | 'error' | 'warning' | 'idle';
+
+  function pickTone(failedCount: number, pipeline: PipelineStatus[]): Tone {
+    if (failedCount > 0) return 'error';
+    const hasPendingBacklog = pipeline.some(
+      (p) => p.status === 'pending' && p.count > 10,
+    );
+    if (hasPendingBacklog) return 'warning';
+    return 'success';
+  }
+
+  const TONE_CLASS: Record<Tone, string> = {
+    success: 'bg-success',
+    error: 'bg-error',
+    warning: 'bg-warning',
+    idle: 'bg-default',
+  };
+
+  const TONE_LABEL: Record<Tone, string> = {
+    success: '정상',
+    error: '실패 있음',
+    warning: '대기열 적체',
+    idle: '확인 중',
+  };
+
+  let tone: Tone = $derived(
+    $dashboardSummary
+      ? pickTone($dashboardSummary.failed_count, $dashboardSummary.pipeline_status)
+      : 'idle',
+  );
+
+  function buildStageRows(pipeline: PipelineStatus[]) {
+    // stage별로 status 카운트 합산 (extract/classify/embed/preview 등)
+    const grouped = new Map<string, Record<string, number>>();
+    for (const p of pipeline) {
+      const cur = grouped.get(p.stage) ?? {};
+      cur[p.status] = (cur[p.status] ?? 0) + p.count;
+      grouped.set(p.stage, cur);
+    }
+    return [...grouped.entries()].map(([stage, counts]) => ({
+      stage,
+      pending: counts.pending ?? 0,
+      processing: counts.processing ?? 0,
+      failed: counts.failed ?? 0,
+    }));
+  }
+
+  let stageRows = $derived(
+    $dashboardSummary ? buildStageRows($dashboardSummary.pipeline_status) : [],
+  );
+
+  function buildTooltip(
+    summary: DashboardSummary | null,
+    rows: ReturnType<typeof buildStageRows>,
+    currentTone: Tone,
+  ): string {
+    if (!summary) return '시스템 상태 확인 중';
+    const head = `시스템: ${TONE_LABEL[currentTone]} (실패 ${summary.failed_count})`;
+    if (rows.length === 0) return head;
+    const lines = rows.map(
+      (r) => `${r.stage}: 대기 ${r.pending} · 처리 ${r.processing} · 실패 ${r.failed}`,
+    );
+    return [head, ...lines].join('\n');
+  }
+
+  let tooltipText = $derived(buildTooltip($dashboardSummary, stageRows, tone));
+</script>
+
+<span
+  class="inline-flex h-2 w-2 rounded-full {TONE_CLASS[tone]}"
+  role="img"
+  aria-label={TONE_LABEL[tone]}
+  title={tooltipText}
+></span>

frontend/src/lib/stores/system.ts

@@ -0,0 +1,79 @@
+// 시스템 상태 store — Phase B에서 신규.
+// /dashboard/ API 응답을 60초 주기로 폴링하고, 첫 subscribe 시 자동 시작한다.
+// SystemStatusDot(B)과 dashboard(C)가 같은 fetch를 공유해 중복 호출을 방지.
+//
+// API 응답 shape: app/api/dashboard.py DashboardResponse 참조
+
+import { writable } from 'svelte/store';
+import { api } from '$lib/api';
+
+export interface DomainCount {
+  domain: string | null;
+  count: number;
+}
+
+export interface RecentDocument {
+  id: number;
+  title: string | null;
+  file_format: string;
+  ai_domain: string | null;
+  created_at: string;
+}
+
+export interface PipelineStatus {
+  stage: string;
+  status: string;
+  count: number;
+}
+
+export interface DashboardSummary {
+  today_added: number;
+  today_by_domain: DomainCount[];
+  inbox_count: number;
+  law_alerts: number;
+  recent_documents: RecentDocument[];
+  pipeline_status: PipelineStatus[];
+  failed_count: number;
+  total_documents: number;
+}
+
+const POLL_INTERVAL_MS = 60_000;
+
+let pollHandle: ReturnType<typeof setInterval> | null = null;
+let subscriberCount = 0;
+let inFlight: Promise<void> | null = null;
+
+const internal = writable<DashboardSummary | null>(null, (_set) => {
+  // svelte writable의 두 번째 인자는 첫 구독 시 호출되는 start fn,
+  // 반환값은 마지막 unsubscribe 시 호출되는 stop fn.
+  subscriberCount += 1;
+  if (subscriberCount === 1) {
+    void refresh();
+    pollHandle = setInterval(() => void refresh(), POLL_INTERVAL_MS);
+  }
+  return () => {
+    subscriberCount -= 1;
+    if (subscriberCount === 0 && pollHandle) {
+      clearInterval(pollHandle);
+      pollHandle = null;
+    }
+  };
+});
+
+export const dashboardSummary = { subscribe: internal.subscribe };
+
+export async function refresh(): Promise<void> {
+  // 동시 fetch 합치기 — 폴링 + 수동 새로고침이 겹쳐도 1회만
+  if (inFlight) return inFlight;
+  inFlight = (async () => {
+    try {
+      const data = await api<DashboardSummary>('/dashboard/');
+      internal.set(data);
+    } catch (err) {
+      console.error('대시보드 폴링 실패:', err);
+    } finally {
+      inFlight = null;
+    }
+  })();
+  return inFlight;
+}

frontend/src/routes/+layout.svelte

@@ -3,9 +3,15 @@
   import { browser } from '$app/environment';
   import { page } from '$app/stores';
   import { goto } from '$app/navigation';
+  import { Menu } from 'lucide-svelte';
   import { isAuthenticated, user, tryRefresh, logout } from '$lib/stores/auth';
   import { toasts, removeToast } from '$lib/stores/toast';
+  import { ui } from '$lib/stores/uiState.svelte';
   import Sidebar from '$lib/components/Sidebar.svelte';
+  import SystemStatusDot from '$lib/components/SystemStatusDot.svelte';
+  import Button from '$lib/components/ui/Button.svelte';
+  import IconButton from '$lib/components/ui/IconButton.svelte';
+  import Drawer from '$lib/components/ui/Drawer.svelte';
   import '../app.css';
 
   const PUBLIC_PATHS = ['/login', '/setup', '/__styleguide'];
@@ -20,26 +26,14 @@
   };
 
   let authChecked = $state(false);
-  let sidebarOpen = $state(false);
 
   onMount(async () => {
-    // localStorage에서 사이드바 상태 복원
-    const saved = localStorage.getItem('sidebarOpen');
-    if (saved === 'true') sidebarOpen = true;
-
     if (!$isAuthenticated) {
       await tryRefresh();
     }
     authChecked = true;
   });
 
-  // 사이드바 상태 저장
-  $effect(() => {
-    if (browser) {
-      localStorage.setItem('sidebarOpen', String(sidebarOpen));
-    }
-  });
-
   $effect(() => {
     if (browser && authChecked && !$isAuthenticated && !PUBLIC_PATHS.some(p => $page.url.pathname.startsWith(p))) {
       goto('/login');
@@ -53,8 +47,9 @@
       e.preventDefault();
       document.querySelector('[data-search-input]')?.focus();
     }
-    if (e.key === 'Escape' && sidebarOpen) {
-      sidebarOpen = false;
+    if (e.key === 'Escape') {
+      // 5대 원칙 #2 — 글로벌 Esc는 uiState에 위임 (modal stack → drawer 우선순위 자동 처리)
+      ui.handleEscape();
     }
   }
 </script>
@@ -72,46 +67,32 @@
       <nav class="flex items-center justify-between px-4 py-2 border-b border-default bg-surface shrink-0">
         <div class="flex items-center gap-3">
           {#if !$page.url.pathname.startsWith('/news')}
-          <button
-            onclick={() => sidebarOpen = !sidebarOpen}
-            class="p-1.5 rounded-md hover:bg-default text-dim"
-            aria-label="사이드바 토글"
-          >
-            <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
-              <path d="M3 12h18M3 6h18M3 18h18"/>
-            </svg>
-          </button>
+            <IconButton
+              icon={Menu}
+              size="sm"
+              aria-label="사이드바 토글"
+              onclick={() => ui.openDrawer('sidebar')}
+            />
           {/if}
           <a href="/" class="text-sm font-semibold hover:text-accent">PKM</a>
           <span class="text-dim text-xs">/</span>
           <a href="/documents" class="text-xs hover:text-accent">문서</a>
+          <SystemStatusDot />
         </div>
-        <div class="flex items-center gap-3">
-          <a href="/news" class="text-xs text-dim hover:text-text">뉴스</a>
-          <a href="/inbox" class="text-xs text-dim hover:text-text">Inbox</a>
-          <a href="/settings" class="text-xs text-dim hover:text-text">설정</a>
-          <button
-            onclick={() => logout()}
-            class="text-xs text-dim hover:text-text"
-          >로그아웃</button>
+        <div class="flex items-center gap-1">
+          <Button variant="ghost" size="sm" href="/news">뉴스</Button>
+          <Button variant="ghost" size="sm" href="/inbox">Inbox</Button>
+          <Button variant="ghost" size="sm" href="/settings">설정</Button>
+          <Button variant="ghost" size="sm" onclick={() => logout()}>로그아웃</Button>
         </div>
       </nav>
 
       <!-- 메인 -->
       <div class="flex-1 min-h-0 relative">
-        <!-- 사이드바 오버레이 (모든 화면에서 동일) -->
-        {#if sidebarOpen}
-          <div class="fixed inset-0 z-40">
-            <button
-              onclick={() => sidebarOpen = false}
-              class="absolute inset-0 bg-black/40"
-              aria-label="사이드바 닫기"
-            ></button>
-            <div class="absolute left-0 top-0 bottom-0 z-50" style="width: var(--sidebar-w)">
-              <Sidebar />
-            </div>
-          </div>
-        {/if}
+        <!-- 사이드바 드로어 (모든 화면에서 동일, uiState 단일 slot 관리) -->
+        <Drawer id="sidebar" side="left" width="sidebar" aria-label="사이드바">
+          <Sidebar />
+        </Drawer>
 
         <!-- 콘텐츠 -->
         <main class="h-full overflow-hidden">