fix: search endpoint — correct column name and DISTINCT/ORDER BY

- Fix Photo.created_at → Photo.added_at (column doesn't exist)
- Fix Postgres DISTINCT + ORDER BY conflict by using a subquery for
  tag_id filtering instead of JOIN + DISTINCT on the outer query

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

backend/app/services/search.py

@@ -102,12 +102,16 @@ async def hybrid_search(
 
     # If no text query, fall back to recent photos
     if not q:
-        stmt = select(Photo.id).order_by(Photo.created_at.desc())
         if tag_ids:
             from app.models.tags import photo_tags
-            stmt = stmt.join(photo_tags, Photo.id == photo_tags.c.photo_id).where(
+            # Subquery to get distinct photo_ids matching the tag filter
+            sub = select(photo_tags.c.photo_id).where(
                 photo_tags.c.tag_id.in_(tag_ids)
-            ).distinct()
+            ).distinct().subquery()
+            stmt = select(Photo.id).join(sub, Photo.id == sub.c.photo_id)
+        else:
+            stmt = select(Photo.id)
+        stmt = stmt.order_by(Photo.added_at.desc())
         if date_from:
             stmt = stmt.where(Photo.taken_at >= date_from)
         if date_to: