feat(core): track the mic voiceprint sample on RecordingSession

mic_voice_sample carries the VoiceSample handle from start_recording
through to stop_recording so the final diarization pass can run the
mic-speaker voiceprint match.

src-tauri/src/lib.rs

@@ -78,6 +78,12 @@ pub struct RecordingSession {
     /// (T4.4, FR-SPK-2). Never rewritten onto segments (FR-SPK-5); resolved
     /// at render/finalize time instead.
     pub speaker_names: Arc<StdMutex<std::collections::HashMap<String, String>>>,
+    /// A few seconds of raw mic-only audio, captured once early in the
+    /// recording — used at `stop_recording` to voiceprint-match the mic
+    /// against the diarized speaker clusters so the mic speaker can be
+    /// auto-labeled "You" instead of a clustered "S1"/"S2". `None` when the
+    /// mic is disabled (same conditions as `mic_capture`).
+    pub mic_voice_sample: Option<Arc<audio::VoiceSample>>,
 }
 
 /// Wraps the tray icon so it can be looked up from commands to update its