[MBL-19553][Student] Add comprehensive test coverage for ToDoList feature

Added unit tests and Compose UI tests to verify CalendarSharedEvents
integration and empty state behavior with removingItemIds filtering.

Changes:
- Added ToDoListScreenTest.kt with 18 Compose UI tests covering all
  states (loading, error, empty, with items), filtering, and interactions
- Made ToDoListContent internal with testTags for testability
- Added tests in ToDoListViewModelTest.kt for:
  * Account-level calendar events clickability
  * RefreshToDoList event triggering data reload
  * Empty state when completing last item via swipe/checkbox
- Added tests in EditDashboardViewModelTest.kt for:
  * RefreshToDoList event when adding/removing courses from favorites

Test plan:
- Run unit tests: ./gradle/gradlew :libs:pandautils:test
- Run UI tests: ./gradle/gradlew :libs:pandautils:connectedDebugAndroidTest
- Verify all tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kristofnemere