feat: TMDB Discover source + retry yt-dlp once before fallback (v1.0.0.17)

The fixed TV lists are mostly long-running shows whose first_air_date is
outside ReleaseDateRangeMonths, and paging stops at the first page with no
in-range title, so only ~7 TV candidates were found (5 then dropped by
language). Add a "discover" source per media type that asks /discover for
recent titles in AllowedLanguages, sorted by popularity (1600+ TV results
for en|fr today). TV Discover defaults on, movie Discover off.

yt-dlp failures were mostly passing HTTP 403s from back-to-back requests;
the built-in fallback is sometimes only offered 360p. Retry yt-dlp once
after 15s before falling back.

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

Jellyfin.Plugin.CinemaTrailers4Jellyfins/Configuration/PluginConfiguration.cs

@@ -14,6 +14,8 @@ namespace Jellyfin.Plugin.CinemaTrailers4Jellyfins.Configuration
         public bool SourceUpcoming { get; set; } = true;
         public bool SourcePopular { get; set; } = false;
         public bool SourceTopRated { get; set; } = false;
+        // TMDB Discover: newest titles in the allowed languages, most popular first.
+        public bool SourceDiscover { get; set; } = false;
 
         // ── Sources (TV Shows) ───────────────────────────────────────────────
 
@@ -21,6 +23,9 @@ namespace Jellyfin.Plugin.CinemaTrailers4Jellyfins.Configuration
         public bool SourceTvOnTheAir { get; set; } = true;
         public bool SourceTvPopular { get; set; } = false;
         public bool SourceTvTopRated { get; set; } = false;
+        // TMDB Discover: newest shows in the allowed languages, most popular first. On by default:
+        // the TV lists above are mostly long-running shows the date range filters out.
+        public bool SourceTvDiscover { get; set; } = true;
 
         // ── Date Range ────────────────────────────────────────────────────────