docs: update links and enhance MQTT implementation guide

Author: agessaman

CHANGELOG.md

@@ -1,7 +1,7 @@
 # MeshCore Observer — Changelog
 
 Changes to the MQTT observer / bridge work that powers the firmware offered on
-[flasher.meshcore.io](https://flasher.meshcore.io). Newest changes are at the top.
+[observer.gessaman.com](https://observer.gessaman.com/). Newest changes are at the top.
 
 **Legend:** **New** = new capability · **Fix** = bug fix · **Improvement** = enhancement to
 existing behavior · **Internal** = refactor / under-the-hood · **Docs** = documentation ·