This commit introduces two major user experience enhancements:

1.  **Task Cancellation:**
    - Users can now interrupt long-running AI tasks (both interim message generation and full agent execution) via a 'Stop Agent' button.
    - Implemented using a cooperative `threading.Event` passed from the controller to the service layer, ensuring graceful termination.
    - A custom `TaskInterruptedException` is raised and handled to update the UI state accordingly.

2.  **Copy Message to Clipboard:**
    - A copy icon has been added to each chat message (both user and agent).
    - Clicking the icon copies the full raw message content to the system clipboard and displays a confirmation snackbar.

These features significantly improve the application's robustness and usability, giving users greater control over the agent's operations.