Allow users to end an interview immediately without generating a report

[jin11109]

Description

After a mock interview ends, users must wait for the evaluation report before they can leave or start another interview.

Add a “Skip report and exit” option to the report-generation screen. This should let users immediately end the session without waiting for, displaying, or saving the report.

Suggested confirmation:

End this interview without waiting for a report? Any report in progress will be discarded and will not be saved.

Suggested implementation

Frontend

Add the action to the ending overlay in web/interview.html.

In web/interview.js, the handler should:

• Mark the session as intentionally terminated.
• Clear the ending and report timers.
• Stop local media, integrity monitoring, and other session resources.
• Send a skip-report signal when possible.
• Disconnect from the LiveKit room.
• Return to the home page.
• Ignore any report that arrives after the session has been terminated.
• Avoid creating an offline summary or report-history entry.

Existing cleanup logic such as stopEndingEscape(), stopEndingClock(), stopLocalMedia(), and room disconnection can be reused.

Backend

Report generation is currently awaited directly inside the interview event handler. While it is running, that handler cannot process a later cancellation message or candidate-disconnection event.

To support cancellation:

1. Run report generation as a cancellable task while allowing the room event loop to continue.
2. Add a cancellation signal for an explicit skip request or candidate disconnection.
3. Race report completion against that signal using a cancellation token or tokio::select!.
4. If cancellation wins, discard the result, do not publish a report, and clean up the session.

Cancellation should be best-effort because an external model request may already have started, but the application should stop waiting for it and must not publish or save its result.

[janice-0]

I think we could add a "Generate report" button to the interview interface and let users decide for themselves.
There would be two cases:

1. Generate evaluation report: The frontend sends a request_report signal. The backend starts generating the report and saves the record only after receiving it.
2. Leave without a report: The frontend sends skip_report, then disconnects and returns to the home page. The backend neither generates nor saves a report.

[Corn0722]

I think there could be one more case to consider: allowing users to generate and view the report without saving it to their report history.

For example, users may only want to test the system, or an unexpected event during the interview may lead to a poor interview result. In such cases, users may still want to generate and review the report, but not necessarily save it in their history.

This would give users three options:

                    ┌── Generate & save report
                    │
Interview ends ─────┼── Generate but don't save
                    │
                    └── Skip report

For the implementation, the frontend could send whether the report should be saved along with the report request. The backend would then generate and publish the report as usual, but only save it to the report history when the user chooses to save it. The existing skip_report flow could remain unchanged for users who don't want to generate the report at all.