fix: replace deprecated regex with pattern in search Query param

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

app/api/search.py

@@ -42,7 +42,7 @@ async def search(
     q: str,
     user: Annotated[User, Depends(get_current_user)],
     session: Annotated[AsyncSession, Depends(get_session)],
-    mode: str = Query("hybrid", regex="^(fts|trgm|vector|hybrid)$"),
+    mode: str = Query("hybrid", pattern="^(fts|trgm|vector|hybrid)$"),
     limit: int = Query(20, ge=1, le=100),
 ):
     """문서 검색