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/server/server.go

@@ -138,6 +138,7 @@ func (s *Server) Handler() http.Handler {
 	api("PUT /api/items/{id}", s.apiUpdateItem)
 	api("POST /api/items/{id}/image", s.apiUploadItemImage)
 	api("POST /api/items/{id}/move", s.apiMoveItem)
+	api("POST /api/items/{id}/refresh", s.apiRefreshItem)
 	api("DELETE /api/items/{id}", s.apiDeleteItem)
 	api("GET /api/search", s.apiSearch)
 	api("GET /api/settings", s.apiSettings)