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>

frontend/src/api/index.js

@@ -129,6 +129,7 @@ export const getCommunityShelf = () => api.get("/discovery/community");
 
 // Stats
 export const getStats = () => api.get("/stats");
+export const deleteTasteTag = (tag) => api.delete(`/stats/taste/${encodeURIComponent(tag)}`);
 
 // Admin
 export const getAdminUsers = () => api.get("/admin/users");