refactor: 사이드바를 전역 레이아웃으로 이동

- +layout.svelte: 사이드바 + 상단 nav 통합 (로그인/셋업 제외)
- 각 페이지 중복 nav 제거 (dashboard, documents, detail, inbox, settings)
- 모바일 drawer + ESC 닫기 전역 처리

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/routes/+page.svelte

@@ -2,8 +2,7 @@
   import { onMount } from 'svelte';
   import { goto } from '$app/navigation';
   import { api } from '$lib/api';
-  import { isAuthenticated, user, logout } from '$lib/stores/auth';
-  import { sidebarOpen, addToast } from '$lib/stores/ui';
+  import { addToast } from '$lib/stores/ui';
 
   let dashboard = null;
   let loading = true;
@@ -19,25 +18,8 @@
   });
 </script>
 
-<div class="min-h-screen">
-  <!-- 상단 네비게이션 -->
-  <nav class="flex items-center justify-between px-6 py-3 border-b border-[var(--border)] bg-[var(--surface)]">
-    <div class="flex items-center gap-4">
-      <button onclick={() => sidebarOpen.update(v => !v)} class="text-[var(--text-dim)] hover:text-[var(--text)]">
-        &#9776;
-      </button>
-      <h1 class="text-lg font-semibold">hyungi Document Server</h1>
-    </div>
-    <div class="flex items-center gap-4">
-      <a href="/documents" class="text-sm text-[var(--text-dim)] hover:text-[var(--text)]">문서</a>
-      <a href="/inbox" class="text-sm text-[var(--text-dim)] hover:text-[var(--text)]">Inbox</a>
-      <span class="text-sm text-[var(--text-dim)]">{$user?.username}</span>
-      <button onclick={() => { logout(); goto('/login'); }} class="text-sm text-[var(--error)] hover:underline">로그아웃</button>
-    </div>
-  </nav>
-
-  <!-- 대시보드 -->
-  <div class="max-w-6xl mx-auto p-6">
+<div class="p-4 lg:p-6">
+  <div class="max-w-6xl mx-auto">
     <h2 class="text-xl font-bold mb-6">대시보드</h2>
 
     {#if loading}