Implement account deletion handling and improve user feedback

- Added checks for accounts marked for deletion in signup, verification, and password reset processes.
- Updated reward and task listing to sort user-created items first.
- Enhanced user API to clear verification and reset tokens when marking accounts for deletion.
- Introduced tests for marked accounts to ensure proper handling in various scenarios.
- Updated profile and reward edit components to reflect changes in validation and data handling.

backend/api/user_api.py

@@ -231,6 +231,13 @@ def mark_for_deletion():
     # Mark for deletion
     user.marked_for_deletion = True
     user.marked_for_deletion_at = datetime.now(timezone.utc).isoformat()
+
+    # Invalidate any outstanding verification/reset tokens so they cannot be used after marking
+    user.verify_token = None
+    user.verify_token_created = None
+    user.reset_token = None
+    user.reset_token_created = None
+
     users_db.update(user.to_dict(), UserQuery.id == user.id)
     
     # Trigger SSE event