feat: Phase 1B — DocumentCard/TagPill/FormatIcon 컴포넌트

- DocumentCard: 포맷 아이콘, 제목+요약, domain 경로, 태그 pill,
  data_origin 배지, 날짜, 파일 크기
- TagPill: 계층별 색상 (@amber, #blue, $green, !red), 클릭→필터
- FormatIcon: 파일 포맷별 lucide 아이콘 매핑
- documents 페이지에서 DocumentCard 컴포넌트 사용

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

frontend/src/routes/documents/+page.svelte

@@ -3,6 +3,7 @@
   import { goto } from '$app/navigation';
   import { api } from '$lib/api';
   import { addToast } from '$lib/stores/ui';
+  import DocumentCard from '$lib/components/DocumentCard.svelte';
 
   let documents = $state([]);
   let total = $state(0);
@@ -182,36 +183,7 @@
   {:else}
     <div class="space-y-1.5">
       {#each items as doc}
-        <a
-          href="/documents/{doc.id}"
-          class="flex items-center justify-between p-3 bg-[var(--surface)] border border-[var(--border)] rounded-lg hover:border-[var(--accent)] transition-colors group"
-        >
-          <div class="flex items-center gap-3 min-w-0">
-            <span class="text-[10px] px-1.5 py-0.5 rounded bg-[var(--border)] text-[var(--text-dim)] uppercase shrink-0 font-mono">{doc.file_format}</span>
-            <div class="min-w-0">
-              <p class="text-sm font-medium truncate group-hover:text-[var(--accent)]">{doc.title || '제목 없음'}</p>
-              <div class="flex items-center gap-2 mt-0.5">
-                {#if doc.ai_domain}
-                  <span class="text-[10px] text-[var(--text-dim)]">{doc.ai_domain.replace('Knowledge/', '')}{doc.ai_sub_group ? ` / ${doc.ai_sub_group}` : ''}</span>
-                {/if}
-                {#if doc.ai_summary}
-                  <span class="text-[10px] text-[var(--text-dim)] truncate max-w-xs hidden sm:inline">· {doc.ai_summary?.slice(0, 80)}</span>
-                {/if}
-              </div>
-            </div>
-          </div>
-          <div class="flex items-center gap-2 shrink-0 ml-3">
-            {#if doc.ai_tags?.length}
-              <span class="text-[10px] text-[var(--accent)] hidden md:inline">{doc.ai_tags[0]}</span>
-            {/if}
-            {#if doc.score !== undefined}
-              <span class="text-[10px] text-[var(--accent)]">{(doc.score * 100).toFixed(0)}%</span>
-            {/if}
-            {#if doc.data_origin}
-              <span class="text-[10px] px-1.5 py-0.5 rounded {doc.data_origin === 'work' ? 'bg-blue-900/30 text-blue-400' : 'bg-gray-800 text-gray-400'}">{doc.data_origin}</span>
-            {/if}
-          </div>
-        </a>
+        <DocumentCard {doc} showDomain={!filterDomain} />
       {/each}
     </div>