Releases: VERSION + automatic patch tags + promote; updater installs newer versions (node-26#49)

VERSION holds MAJOR.MINOR (1.1), edited by hand. Every push to main is
tagged vMAJOR.MINOR.PATCH by the "Tag release" workflow, with PATCH counted
as an integer by scripts/next-version.sh. "Promote release" moves the major
tag (v1) to a tested release and refuses to move it backwards.

drb-update.sh: a newer release on the node's channel is now a reason to
update by itself. REF=latest follows the highest vX.Y.Z tag (test nodes);
REF=v1 follows the promoted tag (customer nodes). Versions compare per
field as integers (1.10.0 > 1.9.3, never string or float order). It never
downgrades, and an untagged target still needs a request. After an update
it writes DRB_VERSION to .env; the edge node reports it in checkin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-edge-node/app/internal/mqtt_manager.py

@@ -378,6 +378,7 @@ class MQTTManager:
             "enforce_override_timeout": config.enforce_override_timeout,
             "secondary_sdr_mode": config.secondary_sdr_mode,
             "secondary_sdr_priority": config.secondary_sdr_priority,
+            "version": settings.drb_version,
         }
         payload["sdr_pins"] = config.sdr_pins
         # Conventional channels (node-26#24): name/freq/NAC and whether the