Add delete button to taste profile tags in Stats

- Backend: DELETE /stats/taste/{tag} removes the row from user_tag_affinity
- API: deleteTasteTag(tag) helper
- Stats UI: × button on each tag chip, faint by default, full opacity on hover;
  invalidates stats query so the tag disappears immediately

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/routers/stats.py

@@ -1,10 +1,10 @@
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, HTTPException
 from sqlalchemy.orm import Session
 from sqlalchemy import text
 
 from ..auth_utils import get_current_user
 from ..database import get_db
-from ..models import User
+from ..models import User, UserTagAffinity
 
 router = APIRouter()
 
@@ -142,3 +142,16 @@ def get_stats(
         "top_categories": [dict(r) for r in top_categories],
         "taste_profile": [dict(r) for r in taste_profile],
     }
+
+
+@router.delete("/taste/{tag}", status_code=204)
+def delete_taste_tag(
+    tag: str,
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    row = db.query(UserTagAffinity).filter_by(user_id=current_user.id, tag=tag).first()
+    if not row:
+        raise HTTPException(status_code=404, detail="Tag not found")
+    db.delete(row)
+    db.commit()