feat(core,app,android,ios): play the dialogue, not the signs and songs

Anime releases often carry two subtitle tracks in one language, the
dialogue and a "Signs & Songs" track, and the second is as often as not
the one marked default or forced. mpv, picking by language, played it.

pstr_core::subtitles reads a track's name and forced flag for whether it
is the dialogue, and every client asks it once per file, after mpv has
made its own pick, whether to switch to a track in the same language
that is. A subtitle track the viewer chose by name stays, and subtitles
that are off stay off.

crates/pstr-android/src/lib.rs

@@ -27,6 +27,7 @@ use pstr_core::proton_drive_rs::ThumbnailType;
 use pstr_core::proton_sdk::api::HumanVerificationCredential;
 use pstr_core::proton_sdk::ids::{LinkId, VolumeId};
 use pstr_core::shares::AccountFolder;
+use pstr_core::subtitles::SubtitleTrack;
 use pstr_core::sync::WatchSync;
 use pstr_core::{
     Account, AccountStore, SecretStore, Share, ShareClient, ShareStore, SharedLibrary,
@@ -739,6 +740,38 @@ fn chapter_kind(role: ChapterRole) -> ChapterKind {
     }
 }
 
+/// One subtitle track as the player read it out of mpv's `track-list`.
+#[derive(Debug, Clone, uniffi::Record)]
+pub struct SubtitleTrackRecord {
+    pub id: i64,
+    pub language: Option<String>,
+    pub title: Option<String>,
+    pub default: bool,
+    pub forced: bool,
+    pub selected: bool,
+}
+
+/// The dialogue track to play in place of the subtitle track mpv chose, when
+/// mpv chose the signs and songs (`pstr_core::subtitles`). Asked once per file,
+/// as soon as mpv has loaded it and made its own pick.
+#[uniffi::export]
+pub fn full_subtitles_instead(tracks: Vec<SubtitleTrackRecord>) -> Option<i64> {
+    let tracks: Vec<SubtitleTrack> = tracks
+        .into_iter()
+        .map(|track| SubtitleTrack {
+            id: track.id,
+            language: track
+                .language
+                .filter(|language| !language.trim().is_empty()),
+            title: track.title.filter(|title| !title.trim().is_empty()),
+            default: track.default,
+            forced: track.forced,
+            selected: track.selected,
+        })
+        .collect();
+    pstr_core::subtitles::full_instead(&tracks)
+}
+
 /// What the app is holding on disk. Offline episodes are the viewer's, the
 /// block cache is not: only the latter may be reclaimed without asking.
 #[derive(Debug, Clone, uniffi::Record)]