feat(models): add graph_calendar Settings fields (T8.9, M4.4)

src-tauri/src/models.rs

@@ -242,6 +242,13 @@ pub struct Settings {
     pub pst_last_path: Option<String>,
     #[serde(default)]
     pub pst_auto_sync: bool,
+    // Microsoft Graph calendar source (M4.4, T8.9, ADR-0008, FR-CAL-6). Opt-in,
+    // explicit consent via OAuth PKCE — off by default. The credential ref
+    // points into the OS credential store; the token itself never lives here.
+    #[serde(default)]
+    pub graph_calendar_enabled: bool,
+    #[serde(default)]
+    pub graph_calendar_credential_ref: Option<String>,
     // Audio capture device override (FR-CAP-1). `Device::get_id()` string;
     // None = system default render device (loopback / system audio).
     #[serde(default)]