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/infrastructure/api.rs

@@ -33,7 +33,10 @@ pub struct ApiClient {
     token_path: PathBuf,
 }
 
-const SCOPES: &[&str] = &["https://www.googleapis.com/auth/tasks"];
+const SCOPES: &[&str] = &[
+    "https://www.googleapis.com/auth/tasks",
+    "https://www.googleapis.com/auth/calendar.readonly",
+];
 
 impl ApiClient {
     pub async fn new(secret_path: impl AsRef<Path>) -> Result<Self, ApiError> {
@@ -455,4 +458,60 @@ impl ApiClient {
 
         Ok(())
     }
+
+    pub async fn fetch_upcoming_events(&self, max_results: u32) -> Result<Vec<CalendarEvent>, ApiError> {
+        let token = self.get_token().await?;
+
+        let now = chrono::Utc::now();
+        let week_later = now + chrono::Duration::days(7);
+
+        let resp = self
+            .client
+            .get("https://www.googleapis.com/calendar/v3/calendars/primary/events")
+            .bearer_auth(&token)
+            .query(&[
+                ("orderBy", "startTime"),
+                ("singleEvents", "true"),
+                ("timeMin", &now.format("%Y-%m-%dT%H:%M:%SZ").to_string()),
+                ("timeMax", &week_later.format("%Y-%m-%dT%H:%M:%SZ").to_string()),
+                ("maxResults", &max_results.to_string()),
+            ])
+            .send()
+            .await
+            .map_err(|e| ApiError::Network(e.to_string()))?;
+
+        if !resp.status().is_success() {
+            let status = resp.status();
+            let body = resp.text().await.unwrap_or_default();
+            return Err(ApiError::Api(format!("Calendar fetch failed: {} - {}", status, body)));
+        }
+
+        let body: serde_json::Value = resp.json().await
+            .map_err(|e| ApiError::Api(format!("Calendar JSON parse error: {}", e)))?;
+
+        let items = body["items"].as_array()
+            .map(|arr| {
+                arr.iter().filter_map(|item| {
+                    let summary = item["summary"].as_str()?.to_string();
+                    let start = parse_calendar_time(&item["start"]);
+                    let end = parse_calendar_time(&item["end"]);
+                    let location = item["location"].as_str().map(|s| s.to_string());
+                    Some(CalendarEvent { summary, start, end, location })
+                }).collect::<Vec<_>>()
+            })
+            .unwrap_or_default();
+
+        Ok(items)
+    }
+}
+
+fn parse_calendar_time(obj: &serde_json::Value) -> Option<chrono::NaiveDateTime> {
+    if let Some(dt) = obj["dateTime"].as_str() {
+        chrono::DateTime::parse_from_rfc3339(dt).ok().map(|d| d.naive_local())
+    } else if let Some(d) = obj["date"].as_str() {
+        chrono::NaiveDate::parse_from_str(d, "%Y-%m-%d").ok()
+            .map(|date| date.and_hms_opt(0, 0, 0).unwrap())
+    } else {
+        None
+    }
 }