Save source descriptions, add "Why it's #N", fix IGDB studio names

Descriptions
- Items keep the source's description (TMDB/TheTVDB overview, IGDB
  summary, Wikipedia intro) in a new items.description column
  (migration 3); editable in the item form
- Deezer/MusicBrainz track counts and album names are now display-only
  hints, not saved as descriptions

Why it's #N
- The owner's note is presented as "Why it's #N" in the editor and the
  public detail view, above an "About" section with the description

IGDB developers
- IGDB credits internal divisions ("Nintendo EAD", "Nintendo EPD
  Production Group No. 8"). A developer whose name shares its first word
  with its parent company is credited to the parent ("Nintendo");
  independently named studios keep their name (Retro Studios, Naughty
  Dog, Landfall Games)
- Fall back to the publisher when IGDB lists no developer

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

internal/server/api.go

@@ -125,6 +125,7 @@ type itemInput struct {
 	Title       string            `json:"title"`
 	Subtitle    string            `json:"subtitle"`
 	Year        string            `json:"year"`
+	Description string            `json:"description"`
 	Note        string            `json:"note"`
 	ExternalURL string            `json:"externalUrl"`
 	Extra       map[string]string `json:"extra"`
@@ -178,6 +179,7 @@ func (s *Server) apiAddItem(w http.ResponseWriter, r *http.Request) {
 	res := providers.Result{
 		Provider: in.Provider, ProviderID: in.ProviderID, Title: in.Title, Subtitle: in.Subtitle,
 		Year: in.Year, ImageURL: in.ImageURL, ExternalURL: in.ExternalURL, Extra: in.Extra,
+		Overview: in.Description,
 	}
 	if in.Details && in.Provider != "" {
 		res = s.fillDetails(ctx, list.Category, res)
@@ -186,7 +188,7 @@ func (s *Server) apiAddItem(w http.ResponseWriter, r *http.Request) {
 	it := store.Item{
 		ListID: listID, Title: res.Title, Subtitle: res.Subtitle, Year: res.Year,
 		Provider: res.Provider, ProviderID: res.ProviderID, ExternalURL: res.ExternalURL,
-		Note: in.Note, Extra: res.Extra,
+		Description: res.Overview, Note: in.Note, Extra: res.Extra,
 	}
 	var warning string
 	if res.ImageURL != "" {
@@ -266,6 +268,7 @@ func (s *Server) apiUpdateItem(w http.ResponseWriter, r *http.Request) {
 	}
 	it := cur
 	it.Title, it.Subtitle, it.Year, it.Note, it.ExternalURL = in.Title, in.Subtitle, in.Year, in.Note, in.ExternalURL
+	it.Description = in.Description
 	if in.Extra != nil {
 		it.Extra = in.Extra
 	}