feat(capture): log undecodable RF frames to stray_frames table

[iceice400]

Summary

• Log undecodable LoRa frames (both Meshtastic and MeshCore decode fail) to a new stray_frames SQLite table — RF metadata only, no relay or re-encode
• GET /api/stray_frames with time/RSSI filters and ?format=csv export
• Dashboard Unknown RF sidebar tab with filters and CSV download
• Background prune via stray_frames.max_retained / retention_hours in the existing cleanup loop

Why

Operators need visibility into on-band traffic that is not Meshtastic or MeshCore without changing the receive/relay pipeline. Stray logging is insert-only on decode failure and does not transmit.

Type

• Feature
• UI
• Bug fix
• Refactor
• Docs
• Installer
• Region support
• Hardware change

Testing

• python -m unittest tests.test_stray_frame_repository -v (6 tests, pass)
• Tested on hardware
• Dashboard tested on device

Test plan

1. Inject or capture a non-Meshtastic LoRa burst on the tuned channel; confirm a row appears in Unknown RF
2. Apply min-RSSI filter; confirm table updates
3. Export CSV downloads filtered rows
4. Set stray_frames.enabled: false; confirm no new rows after restart
5. Confirm normal Meshtastic/MeshCore packets still decode and relay unchanged

Relay / TX impact

Does not change TX or relay behaviour. Stray path runs only when PacketRouter.decode() returns None; meshcore_usb adapt failures are excluded.

Config

stray_frames:
  enabled: true
  max_retained: 10000
  retention_hours: 168

Documented in docs/CONFIGURATION.md.

AI-assisted?

Implemented with AI assistance; unit tests run locally.