viewer: a Cutscenes browser -- the manifest was invisible plumbing

`movie_manifest` has been parsed since the movie-voice work and rendered
nowhere: it resolved a voice bank and that was all. So the only way to find a
cutscene was to hunt `.wmv` files in the ISO tree, where nothing tells you which
mission a file belongs to, whether it has subtitles, or what is said in it.

View ▸ Cutscenes lists all 104 manifest slots with mission/phase, kind, movie,
subtitle track, voice token and telop, and -- the part that needed no new
parsing, only a route -- resolves the captions to a readable TRANSCRIPT with a
language selector. Subtitles were previously burned into the video during
playback and reachable no other way.

Three negatives are shown rather than smoothed over:

* 5 manifest-bound movies have no `.wmv` (logo1-4 and an encoder test clip).
  They are marked and get no Play button instead of one that would fail.
* 9 of 101 movies resolve no English transcript.
* the `.prt` telop overlay is named by the manifest and we have no parser, so
  the reference is shown labelled "not decoded" rather than omitted.

`cutscene_catalog_binds_movies_and_transcripts` pins all of it against the disc
-- 104/101/99/99/22, the exact absent-movie list, 92 transcripts -- because a
browser that quietly dropped these would look complete and be wrong. The counts
independently reproduce docs/re/movie-subtitle-link.md.

Play routes through the normal FileSelected path, so the existing video player
handles it exactly as it would from the tree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/sylpheed-formats/src/movie_subtitle.rs

@@ -25,8 +25,10 @@ use crate::pak::PakArchive;
 
 /// Subtitle language. `pak_code` selects `dat/movie/<code>.pak`; `game_code`
 /// selects `dat/GP_MAIN_GAME_<code>.pak` (the caption text).
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
 pub enum SubLang {
+    /// Default only because the disc's own default is English.
+    #[default]
     English,
     Japanese,
     German,