feat: redesign day picker with expandable calendar, status markers & Playwright E2E testing

- Replace modal calendar with inline expandable calendar widget integrated into the day picker.
- Add status indicator dots (attended/absent/pending) to month calendar grid matching day picker.
- Disable and gray out weekend days in calendar when weekend schedule is turned off.
- Redesign extend bar with integrated handle that aligns with the palette.
- Remove start-to-end timing on Today screen's class time rail, showing only start time.
- Implement Playwright E2E and visual testing suite with multi-screen capture scripts.
- Add cascade DELETE endpoints for subjects and versioned recurring timetable entries.

components/ui/icon-button.tsx

@@ -29,7 +29,7 @@ export function IconButton({ icon, label, onPress, tone = 'soft', disabled = fal
 }
 
 const styles = StyleSheet.create({
-  base: { width: size.touchTargetMin, height: size.touchTargetMin, borderRadius: radius.control, alignItems: 'center', justifyContent: 'center' },
+  base: { width: size.touchTargetMin, height: size.touchTargetMin, borderRadius: radius.control, borderCurve: 'continuous', alignItems: 'center', justifyContent: 'center' },
   disabled: { opacity: 0.48 },
   pressed: { transform: [{ scale: motion.pressedScale }] },
 });