The rolling-release body is what the flasher dropdown serves as changelog.
Drop the stale v1.16.0 experimental blurb and describe the current observer
surface: MeshCore 1.17.1, web config, in-channel OTA, and neighbors.
firmware-notes.html's setup-guide link feeds config.json's notes on the
next production build, so the fix propagates with the webconfig merge.
Kept identical to the MQTT_INTERNALS.md wording on observer-firmware to
avoid a merge conflict.