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>

build.yaml

@@ -1,5 +1,5 @@
 ---
-version: 1.0.0.16
+version: 1.0.0.17
 name: CinemaTrailers4Jellyfins
 guid: b581493e-1046-40ed-b6dc-cb8027624984
 description: >
@@ -12,9 +12,14 @@ category: General
 owner: 514mart
 targetAbi: 10.11.0.0
 changelog:
-  - The built-in downloader no longer picks YouTube's 360p combined file
-    when separate video and audio streams give a better picture. This
-    mostly showed up when yt-dlp failed and the built-in downloader took over
+  - New "Discover" source for TV shows (on by default) and movies (off by
+    default). It asks TMDB for the newest titles in your selected
+    languages, most popular first. The TV lists (Popular, Top Rated, On The
+    Air, Airing Today) are mostly long-running shows that the date range
+    drops, so very few TV trailers were found before
+  - When yt-dlp fails (often a passing HTTP 403 from YouTube), it is tried
+    once more after 15 seconds before the built-in downloader takes over,
+    which YouTube sometimes only offers 360p
 
 dotnetProjects:
   - name: Jellyfin.Plugin.CinemaTrailers4Jellyfins