feat: locoProgramming modes (BigFred dcc-bus or direct Z21)

[keskad]

Summary

• New locoProgramming block in bigfred-wizard.json: mode is bigfred (default) or direct.
• BigFred mode: if both dccBusId and layoutId are set, skip catalogue autodetection and use that command-station id on /api/v1/dcc-bus/{id}/ws.
• Direct mode: the daemon talks UDP CV/POM to locoProgramming.z21.address:port via a new z21-lan crate (spec §6 encode/parse + send-and-await). Programming HTTP APIs stay the same.

Example:

"locoProgramming": {
  "mode": "bigfred",
  "dccBusId": 1,
  "layoutId": 1,
  "z21": { "address": "192.168.0.10", "port": 21105 }
}

Set "mode": "direct" to bypass dcc-bus for decoder CVs.

Test plan

• cargo test --workspace and cargo clippy --all-targets -- -D warnings
• Default config still uses BigFred autodetection
• With dccBusId+layoutId set, About / programming uses that station id
• Direct mode against an RB1110 at the configured UDP address: read/write a CV on the programming track

Made with Cursor