feat: add IIntroProvider for Wholphin/cinema-mode compatibility

Registers TrailerIntroProvider as IIntroProvider. Queries fake-movie
items in the output folder and returns their local trailer extras
(LocalTrailers) as IntroInfo — mirroring jellyfin-plugin-cinemamode's
proven pattern so Wholphin plays the actual trailer, not the 3-second
black placeholder.

Recursion guard: items whose path starts with the output folder are
excluded from intro injection, so Wholphin's getIntros call on the
intro item itself returns empty. Server-scoped query bypasses library
visibility restrictions so hidden trailer libraries still work.

Adds TrailersPerMovie config option (default 1, 0 = disabled).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

build.yaml

@@ -1,5 +1,5 @@
 ---
-version: 1.0.0.0
+version: 1.0.0.2
 name: CinemaTrailers4Jellyfins
 guid: b581493e-1046-40ed-b6dc-cb8027624984
 description: >
@@ -12,10 +12,10 @@ category: General
 owner: 514mart
 targetAbi: 10.11.0.0
 changelog:
-  - Initial release based on Trailers4Jellyfin — TMDB/YouTube trailer downloads,
-    scheduled task, language/date filters, and trailer rotation, repackaged so
-    each trailer ships inside its own fake-movie folder (placeholder video +
-    locked NFO + trailer) for use with a Cinema Mode pre-roll plugin
+  - Add IIntroProvider support — downloaded trailers now play as pre-rolls before
+    movies in Jellyfin clients with cinema mode (Wholphin, etc.); configurable
+    trailers-per-movie count; recursion-safe so the intro items themselves never
+    trigger a second round of intro injection
 
 dotnetProjects:
   - name: Jellyfin.Plugin.CinemaTrailers4Jellyfins