Add interactive release search (M6)

Release listing and grab in the shared arr client, a full-screen release
list (sort, hide rejected, rejection reasons, confirmation before grabbing
rejected releases; Usenet only), and a season/episode picker for Sonarr.
Overlays are now a stack so dialogs can open above the release list.
Add a fake Newznab indexer to the dev setup.

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

internal/radarr/radarr.go

@@ -145,3 +145,8 @@ func TMDBTerm(tmdbID int) string { return "tmdb:" + strconv.Itoa(tmdbID) }
 func (c *Client) Queue(ctx context.Context) ([]arr.QueueItem, error) {
 	return c.QueueWith(ctx, url.Values{"includeMovie": {"true"}})
 }
+
+// Releases runs an interactive search for a library movie.
+func (c *Client) Releases(ctx context.Context, movieID int) ([]arr.Release, error) {
+	return c.Client.Releases(ctx, url.Values{"movieId": {strconv.Itoa(movieID)}})
+}