feat(core): track resolved per-meeting language on RecordingSession (T8.7, M4.2)

src-tauri/src/lib.rs

@@ -63,6 +63,13 @@ pub struct RecordingSession {
     /// can pick a different model than `Settings.whisper_model`).
     pub active_backend: Arc<StdMutex<models::BackendId>>,
     pub model_id: String,
+    /// Resolved transcription language (T8.7, FR-TRX-4): `None` = auto.
+    /// Set by the transcription worker once the engine loads (to the
+    /// request resolved against model capability, e.g. forced "en" for an
+    /// English-only model) and updated after every decode to whatever was
+    /// actually used/detected — `stop_recording` reads the final value to
+    /// persist on the meeting record.
+    pub language: Arc<StdMutex<Option<String>>>,
     /// `None` when diarization models aren't installed yet (T4.7) — live
     /// provisional turns and the final post-stop pass are both skipped, same
     /// graceful-degradation treatment as a missing hardware backend (T4.3).