Add discard recording feature to stop and delete without saving

[dschuld]

Summary

This PR adds a new "discard" feature that allows users to stop a recording and delete it without saving. This complements the existing "stop" action which saves the recording.

Key Changes

• RecordingEngine: Added discard() method that stops the current recording and deletes its file. The method is a no-op when idle and gracefully handles finalize failures since the file is being discarded anyway.
• RecorderScreen UI:
  • Added a new "Discard" button (red delete icon) that appears alongside pause/resume and stop buttons during recording/paused states
  • Implemented a confirmation dialog to prevent accidental discards with "Discard" and "Keep recording" options
• RecorderViewModel: Added discardRecording() method to dispatch the discard action
• RecordingService: Added ACTION_DISCARD handling to call the engine's discard method and clean up the foreground service
• Strings: Added UI text for the discard button, dialog title, dialog message, and keep recording option

Notable Implementation Details

• The discard operation ignores recorder finalization failures since the file is being deleted anyway
• Previously saved recordings are preserved when discarding a new recording attempt
• The feature can be used while recording or paused
• Comprehensive test coverage includes scenarios for discarding while recording, while paused, when idle, after previous saves, with finalize failures, and ability to record again after discarding

https://claude.ai/code/session_01Ex7jFXCfdXG2EUuJ2yR5ej