Implement multi-account search and improve repository fakes

- Extended search to support global queries across all accounts.
- Updated SearchScreen to handle optional account context and unified results.
- Centralized mailbox comparison logic in Mailbox model.
- Added copyWith to Account model.
- Fixed race conditions and incorrect overrides in unit, widget, and integration tests.
- Reached 80% unit test coverage.

next.md

@@ -20,10 +20,11 @@ Then push
 
 ## Tasks
 
-### 1. Multi-account search improvement
+### 1. Implement Undo for Delete and Move actions
 
-Extend the search functionality to allow searching across all accounts.
+Provide a way for users to undo accidental deletions or moves, improving the safety of the application.
 
-- **UI**: Add a search icon to the account list screen or a global search bar.
-- **Repository**: Implement `searchEmailsGlobal` to query all accounts in the database.
-- **Protocol**: For remote search, parallelize IMAP SEARCH across multiple accounts.
+- **Infrastructure**: Implement a `ChangeLog` or similar mechanism to track the last N destructive actions.
+- **UI**: Display a snackbar with an "Undo" button after a delete or move action.
+- **Logic**: Implement the reverse operation (moving back from Trash or to the source folder) when Undo is pressed.
+- **Sync**: Ensure that undo operations correctly interact with the `pending_changes` queue.