feat(models): MeetingBundle.audio_layout (serde default) for portable layout (FR-SPK)

src-tauri/src/models.rs

@@ -214,6 +214,11 @@ pub struct MeetingBundle {
     pub tags: Vec<String>,
     pub speakers: Vec<SpeakerInfo>,
     pub action_items: Vec<ActionItem>,
+    /// `audio.wav` channel layout (FR-SPK/FR-CAP): `"split"` or `"summed"`.
+    /// `default` so bundles exported before this field deserialize as `None`
+    /// (treated as `"summed"`).
+    #[serde(default)]
+    pub audio_layout: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]