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/public.go

@@ -18,6 +18,7 @@ type ItemView struct {
 	Image       string   `json:"image"`
 	ExternalURL string   `json:"link"`
 	Source      string   `json:"source"`
+	Description string   `json:"description"`
 	Note        string   `json:"note"`
 	Badge       string   `json:"badge"` // e.g. theater production
 	Meta        []MetaKV `json:"meta"`
@@ -59,6 +60,7 @@ func itemView(it store.Item, showNotes bool) ItemView {
 		Subtitle:    it.Subtitle,
 		Year:        it.Year,
 		ExternalURL: it.ExternalURL,
+		Description: it.Description,
 		Source:      providerLabels[it.Provider],
 		Badge:       it.Extra["production"],
 		Meta:        []MetaKV{},