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.

.gitignore

@@ -47,3 +47,9 @@ app-example
 
 # Local College Kit API database
 backend/data/
+
+# Playwright & test artifacts
+dist-web/
+screenshots/
+test-results/
+playwright-report/