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>

web/templates/pages/admin_list.html

@@ -14,6 +14,7 @@
     <div class="admin-head-actions">
       <a class="btn btn--ghost" data-bind="public" href="/l/{{.Data.List.Slug}}">{{icon "external"}}View</a>
       {{template "export" .Data.List.Slug}}
+      {{if ne $c.Key "custom"}}<button class="btn btn--ghost" type="button" data-action="refresh-all" title="Pull the latest details and artwork from each entry's source">{{icon "refresh"}}Refresh all</button>{{end}}
       <button class="btn" type="button" data-action="edit-list">{{icon "settings"}}List settings</button>
     </div>
   </header>