Add an MQTT 5 transport example
Ā
KL
2mo ago+513+513+012345678901234567890123456789-1-1-0123456789
Review scope
Stacked on #3519 for the shared example package and CI setup. This diff contains only the MQTT 5 adapter, Mosquitto configuration, broker examples, configuration tests, and MQTT documentation; there are no gRPC implementation changes.
The existing review follow-ups are preserved, including Last Will setup and client-ID isolation. Negative publish acknowledgments, queue-overflow behavior, broker recording/coverage, and production authorization remain open merge gates.
Validation
Six MQTT configuration tests and pre-commit pass after the split; the dedicated CI job also runs the live broker programs.
AI Disclaimer
This PR was developed with the assistance of either Claude or Codex. I've reviewed and verified the changes.