fix: check all fields for unsaved changes on back press

[naveensingh]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

1. Updated the isEventChanged() function to check for:
   • Repeat limit (recurrence end)
   • Attendees
   • Availability (free/busy)
   • Access level (private/public/confidential)
   • Event status (confirmed/tentative/cancelled)
2. Updated the isTaskChanged() function to check for:
   • Repeat limit (recurrence end)

The issue also mentioned the timezone field, but that seems to already work properly.

Tests performed

Tested discarding:

• Repeat limit (recurrence end)
• Attendees
• Availability (free/busy)
• Access level (private/public/confidential)
• Event status (confirmed/tentative/cancelled)

Closes the following issue(s)

• Closes Save/discard changes dialog is not triggered for certain edits #49

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• All checks are passing.