Add post-session summaries and persistent history

[PurpleSentinel]

Parent: #23

Summary

Store useful outcomes such as actual duration, overtime, laps, launch delay, and completion reason for later review.

Acceptance criteria

• Show a concise summary before returning to Ready.
• Use bounded or ring-buffer storage to control flash wear and capacity.
• Recover safely from an interrupted history write.
• Allow history viewing and deletion on the device.
• Define privacy and retention defaults and add corruption tests.

Roadmap group

Data, configuration, and maintenance