[Runner] Log Windows session-end reason

[Yu Leng (moooyo)]

Summary of the Pull Request

Adds diagnostic logging for Windows session-end messages received by the PowerToys Runner tray window.

• Logs WM_QUERYENDSESSION and WM_ENDSESSION.
• Decodes ENDSESSION_CLOSEAPP, ENDSESSION_CRITICAL, and ENDSESSION_LOGOFF.
• Records whether WM_ENDSESSION confirms or cancels session termination.
• Keeps the existing session-end behavior unchanged.

Related investigation: #50169.

PR Checklist

• Closes: PowerToys randomly exits #50169
• Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: No end-user-facing strings were added
• Dev docs: Added/updated
• New binaries: Added on the required places
• Documentation updated: If checked, please file a pull request on the docs repo and link it here

Detailed Description of the Pull Request / Additional comments

PowerToys 0.100.2 reports show the Runner disappearing without a crash event while Command Palette remains active. One hypothesis is that the Runner receives a Windows session-end or Restart Manager close-app request.

The Runner tray window owns the main message loop and already handles these messages through handle_stateless_session_end_message. This change logs the message phase, raw flags, decoded reason, and confirmed/cancelled state before the existing handler runs. Runner log entries already include process and thread identifiers.

Validation Steps Performed

• Ran git diff --check successfully.
• Reviewed the change against the existing Runner session-end handling.
• Build not run; this is a diagnostic logging-only change.