Harden N2K runtime and add Commanded Address conformance

[jakthom]

Summary

• harden client lifecycle, bounded read/write queues, cancellation, panic containment, and runtime health reporting
• strengthen CAN, gateway, fast-packet, ISO transport, codec, and wire-fidelity handling against malformed or adversarial input
• implement PGN 65240 Commanded Address as an exact nine-byte broadcast transport transition with NAME and address validation, immediate reclaim, and fresh contention gating
• add deterministic conformance evidence, current ISO and NMEA baseline documentation, a machine-readable certification record template, and CI coverage
• refresh the README, contribution/security guidance, architecture context, and ADRs for rapid adoption and agent navigation

Commanded Address

PGN 65240 is accepted only after a complete BAM transfer with an exact 64-bit NAME match and a claimable address from 0 through 251. Fast-packet, addressed transport, malformed length, mismatched NAME, current-address, and special-address commands have no effect. A valid command updates the claiming state, immediately broadcasts Address Claim from the new source, and opens a fresh application-write contention window.

Conformance status

The public just conformance-local suite is reproducible engineering evidence. It is not formal NMEA certification. Licensed ISO review, the official NMEA tool and hardware run, assigned manufacturer and product codes, encrypted result submission, and NMEA validation remain external not-run evidence until performed on a real product.

Verification

• go test ./...
• just conformance-local
• just test-race
• just pgn-sync-check
• just lint
• just secure
• git diff --check