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/providers/providers.go

@@ -14,6 +14,9 @@ import (
 	"time"
 )
 
+// maxDescription caps how much of a source's description is kept.
+const maxDescription = 2000
+
 const UserAgent = "Canon/0.1 (self-hosted favorites list; https://git.iamchrisama.com/cdnutter/canon)"
 
 // Result is one search hit, already shaped like a list item.
@@ -25,7 +28,8 @@ type Result struct {
 	Year        string            `json:"year"`
 	ImageURL    string            `json:"imageUrl"`
 	ExternalURL string            `json:"externalUrl"`
-	Overview    string            `json:"overview"`
+	Overview    string            `json:"overview"` // the source's description, saved with the item
+	Hint        string            `json:"hint"`     // extra context for search results only, e.g. "12 tracks"
 	Extra       map[string]string `json:"extra,omitempty"`
 }