Export settings and session data as JSON or CSV

[PurpleSentinel]

Parent: #23

Summary

Allow users to copy portable settings, summaries, and lap data for analysis or backup.

Acceptance criteria

• Define stable JSON and CSV schemas with firmware version metadata.
• Support export over the USB interface without removing the device filesystem.
• Handle empty history and partial records clearly.
• Avoid exposing internal temporary or backup files.
• Add schema and round-trip tests.

Roadmap group

Data, configuration, and maintenance