feat: add live Discord sharing functionality with dynamic habit progress images

- Implemented live card image generation for user habits using canvas.
- Created API endpoints for starting and managing live Discord sharing sessions.
- Added tests for live Discord sharing to ensure functionality and reliability.
- Introduced CSS styles for the live Discord sharing interface.
- Enhanced error handling and state management for Discord message updates.

src/habits/test-fixture.ts

@@ -22,5 +22,5 @@ export function fixture(path = ':memory:') {
     if (response.status !== status) throw new Error(`${method} ${path}: expected ${status}, got ${response.status}: ${JSON.stringify(data)}`);
     return data;
   }
-  return { sqlite, db, app, origin, request, json, setTime: (date: string) => { time = Date.parse(date); }, close: () => sqlite.close() };
+  return { sqlite, db, app, origin, request, json, setTime: (date: string) => { time = Date.parse(date); }, close: () => { app.stopLiveSharing(); sqlite.close(); } };
 }