Support automatic repeated track and rest cycles

[PurpleSentinel]

Parent: #23

Summary

Allow a configured number of track/rest cycles to run as a structured stint plan.

Acceptance criteria

• Configure cycle count or continuous mode.
• Show current cycle and total cycles on Ready and live screens.
• Allow the user to skip, stop, or restart a phase safely.
• Preserve the existing single-cycle behavior as the default.
• Test phase transitions, early termination, and final completion.

Roadmap group

Session workflow and timing