feat(themes): 테마 인덱스/상세 (11 카테고리 · 111 종목)

- seed/themes.py: 반도체/2차전지/바이오/게임/엔터/자동차/금융/조선·방산/플랫폼·AI/유통·소비재/에너지 정적 매핑
- /api/themes (인덱스) + /api/themes/{slug} (종목 카드 + 최신 종가/등락)
- 홈에 ThemeTiles 그리드, /themes/{slug} 상세 페이지

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/app/page.tsx

@@ -1,6 +1,7 @@
 import { MarketsOverview } from "../components/MarketsOverview";
 import { SearchBox } from "../components/SearchBox";
 import { SeedTiles } from "../components/SeedTiles";
+import { ThemeTiles } from "../components/ThemeTiles";
 
 export default function HomePage() {
   return (
@@ -19,6 +20,10 @@ export default function HomePage() {
         <SeedTiles />
       </div>
 
+      <div className="mt-8">
+        <ThemeTiles />
+      </div>
+
       <div className="mt-6">
         <MarketsOverview />
       </div>