Add pause, resume, restart, and abort session controls

[PurpleSentinel]

Parent: #23

Summary

Provide explicit controls for common timing corrections without forcing a full track-to-rest transition.

Acceptance criteria

• Define distinct pause, resume, restart, abort-to-ready, and finish-to-rest actions.
• Require confirmation for destructive actions while preserving fast emergency exit.
• Keep remaining and elapsed values correct across pauses.
• Show the current paused or confirmation state clearly.
• Add deterministic timing and gesture-state tests.

Roadmap group

Session workflow and timing