Feature 3: Read-only Google Calendar panel

- CalendarEvent model with summary, start, end, location
- New scope calendar.readonly in SCOPES
- fetch_upcoming_events() in ApiClient (15 events, next 7 days)
- Focus::Calendar variant, Tab cycle includes Calendar
- Body layout: left column split into Tasks (flex) + Calendar (8)
- render_calendar_panel with day headers and scroll
- refresh_calendar() called on initial sync and Ctrl+R
- Up/Down scroll Calendar panel when focused

src/app.rs

@@ -23,6 +23,7 @@ pub struct SyncStats {
 pub struct App {
     pub lists: Vec<TaskList>,
     pub tasks: Vec<Task>,
+    pub calendar_events: Vec<CalendarEvent>,
     pub selected_list: usize,
     pub selected_task: usize,
     pub focus: Focus,
@@ -38,6 +39,7 @@ pub struct App {
     pub task_list_scroll: u16,
     pub detail_scroll: u16,
     pub notes_scroll: u16,
+    pub calendar_scroll: u16,
     pub db: Arc<Db>,
     #[allow(dead_code)]
     pub api_client: Arc<ApiClient>,
@@ -66,7 +68,7 @@ pub enum SyncCommand {
 }
 
 impl App {
-    pub fn new(db: Arc<Db>, api_client: Arc<ApiClient>, sync_tx: mpsc::Sender<SyncCommand>) -> Self {
+    pub fn new(db: Arc<Db>, api_client: Arc<ApiClient>, sync_tx: mpsc::Sender<SyncCommand>, _calendar_events_shared: Arc<tokio::sync::Mutex<Vec<CalendarEvent>>>) -> Self {
         let has_token = api_client.has_token();
         let (auth_tx, auth_rx) = std_mpsc::channel();
 
@@ -91,6 +93,7 @@ impl App {
         Self {
             lists,
             tasks,
+            calendar_events: Vec::new(),
             selected_list: 0,
             selected_task: 0,
             focus: Focus::Tabs,
@@ -106,6 +109,7 @@ impl App {
             task_list_scroll: 0,
             detail_scroll: 0,
             notes_scroll: 0,
+            calendar_scroll: 0,
             db,
             api_client,
             needs_auth: !has_token,
@@ -282,7 +286,8 @@ impl App {
                 self.focus = match self.focus {
                     Focus::Tabs => Focus::TaskList,
                     Focus::TaskList => Focus::Detail,
-                    Focus::Detail => Focus::Tabs,
+                    Focus::Detail => Focus::Calendar,
+                    Focus::Calendar => Focus::Tabs,
                 };
             }
             KeyCode::Up if key.modifiers.contains(KeyModifiers::ALT) => {
@@ -305,6 +310,9 @@ impl App {
                 Focus::Detail => {
                     self.detail_scroll = self.detail_scroll.saturating_sub(1);
                 }
+                Focus::Calendar => {
+                    self.calendar_scroll = self.calendar_scroll.saturating_sub(1);
+                }
                 _ => {}
             },
             KeyCode::Down => match self.focus {
@@ -317,6 +325,9 @@ impl App {
                 Focus::Detail => {
                     self.detail_scroll += 1;
                 }
+                Focus::Calendar => {
+                    self.calendar_scroll += 1;
+                }
                 _ => {}
             },
             KeyCode::Right => {
@@ -729,7 +740,7 @@ impl App {
                                 self.load_tasks();
                             }
                         }
-                        Focus::TaskList | Focus::Detail => {
+                        Focus::TaskList | Focus::Detail | Focus::Calendar => {
                             if !self.tasks.is_empty() && self.selected_task < self.tasks.len() {
                                 let task = &self.tasks[self.selected_task];
                                 let task_id = task.id.clone();