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/igdb.go

@@ -58,11 +58,32 @@ func (g *igdb) token(ctx context.Context, fresh bool) (string, error) {
 	return c.token, nil
 }
 
+const igdbFields = `fields name,first_release_date,cover.image_id,summary,url,involved_companies.developer,involved_companies.publisher,involved_companies.company.name,involved_companies.company.parent.name,involved_companies.company.parent.parent.name,involved_companies.company.parent.parent.parent.name,platforms.abbreviation,platforms.name;`
+
 func (g *igdb) Search(ctx context.Context, query string) ([]Result, error) {
 	q := strings.NewReplacer(`\`, ``, `"`, `\"`).Replace(query)
-	body := `search "` + q + `";
-fields name,first_release_date,cover.image_id,summary,url,involved_companies.developer,involved_companies.publisher,involved_companies.company.name,involved_companies.company.parent.name,involved_companies.company.parent.parent.name,involved_companies.company.parent.parent.parent.name,platforms.abbreviation,platforms.name;
-limit 25;`
+	return g.query(ctx, `search "`+q+`";
+`+igdbFields+`
+limit 25;`)
+}
+
+// Lookup refreshes one game by its IGDB ID.
+func (g *igdb) Lookup(ctx context.Context, providerID string) (Result, error) {
+	id, err := strconv.ParseInt(providerID, 10, 64)
+	if err != nil {
+		return Result{}, ErrGone
+	}
+	res, err := g.query(ctx, igdbFields+"\nwhere id = "+strconv.FormatInt(id, 10)+";")
+	if err != nil {
+		return Result{}, err
+	}
+	if len(res) == 0 {
+		return Result{}, ErrGone
+	}
+	return res[0], nil
+}
+
+func (g *igdb) query(ctx context.Context, body string) ([]Result, error) {
 	var games []struct {
 		ID               int64  `json:"id"`
 		Name             string `json:"name"`