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/providers/wikipedia.go

@@ -39,13 +39,28 @@ func (w *wikipedia) Search(ctx context.Context, query string) ([]Result, error)
 var leadingYear = regexp.MustCompile(`^(1[5-9]\d\d|20\d\d)\s+`)
 
 func (w *wikipedia) search(ctx context.Context, query string) ([]Result, error) {
+	return w.pages(ctx, url.Values{"generator": {"search"}, "gsrsearch": {query}, "gsrlimit": {"15"}})
+}
+
+// Lookup refreshes one page by its page ID.
+func (w *wikipedia) Lookup(ctx context.Context, providerID string) (Result, error) {
+	res, err := w.pages(ctx, url.Values{"pageids": {providerID}})
+	if err != nil {
+		return Result{}, err
+	}
+	if len(res) == 0 {
+		return Result{}, ErrGone
+	}
+	return res[0], nil
+}
+
+// pages runs a query for pages (a search, or specific page IDs) and shapes
+// them into results.
+func (w *wikipedia) pages(ctx context.Context, which url.Values) ([]Result, error) {
 	q := url.Values{
 		"action":        {"query"},
 		"format":        {"json"},
 		"formatversion": {"2"},
-		"generator":     {"search"},
-		"gsrsearch":     {query},
-		"gsrlimit":      {"15"},
 		"prop":          {"pageimages|description|info|extracts"},
 		"piprop":        {"thumbnail"},
 		"pithumbsize":   {"800"},
@@ -56,10 +71,14 @@ func (w *wikipedia) search(ctx context.Context, query string) ([]Result, error)
 		"exsentences":   {"3"},
 		"exlimit":       {"max"},
 	}
+	for k, v := range which {
+		q[k] = v
+	}
 	var resp struct {
 		Query struct {
 			Pages []struct {
 				PageID      int64  `json:"pageid"`
+				Missing     bool   `json:"missing"`
 				Title       string `json:"title"`
 				Index       int    `json:"index"`
 				Description string `json:"description"`
@@ -78,6 +97,9 @@ func (w *wikipedia) search(ctx context.Context, query string) ([]Result, error)
 	sort.Slice(pages, func(i, j int) bool { return pages[i].Index < pages[j].Index })
 	out := make([]Result, 0, len(pages))
 	for _, p := range pages {
+		if p.Missing {
+			continue
+		}
 		title := p.Title
 		// "Hamilton (musical)" → "Hamilton"
 		if i := strings.LastIndex(title, " ("); i > 0 && strings.HasSuffix(title, ")") {