Add refresh from source for entries and whole lists

- Every provider can look an entry up again by its ID (TMDB, TheTVDB,
  IGDB, Deezer, MusicBrainz, Wikipedia); search and lookup share parsing
- POST /api/items/{id}/refresh re-applies title, subtitle, year,
  description, link, details and artwork. Kept: the "why" note, rank,
  theater production/venue/cast and a theater entry's year, the Deezer
  preview match. Empty source fields don't erase existing values
- New items.image_custom column (migration 4; existing uploads marked)
  records artwork the owner chose; refresh keeps it unless asked
- Refused for custom lists and hand-added entries; entries the source
  dropped are reported, and a refresh whose title shares no words with
  the current one is rejected as a likely bad ID
- Editor: refresh button per row (asks about the owner's own artwork),
  and "Refresh all" with a confirm step, replace-my-art checkbox,
  progress with Stop, and a summary of problems

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/store.go

@@ -113,6 +113,10 @@ CREATE INDEX items_list_rank ON items(list_id, rank);
 	`ALTER TABLE lists ADD COLUMN art TEXT NOT NULL DEFAULT '';`,
 	// The source's description of the item (TMDB overview, IGDB summary…).
 	`ALTER TABLE items ADD COLUMN description TEXT NOT NULL DEFAULT '';`,
+	// Whether the owner chose the artwork (upload, pasted URL, or removed it)
+	// rather than taking the source's; refresh leaves it alone unless asked.
+	`ALTER TABLE items ADD COLUMN image_custom INTEGER NOT NULL DEFAULT 0;
+UPDATE items SET image_custom = 1 WHERE image_source = 'upload';`,
 }
 
 func (s *Store) migrate(ctx context.Context) error {