Merge upstream/dev into mqtt-bridge-implementation-flex

Merge meshcore-dev changes (kiss_modem targets, preamble SF tuning, CI).
Resolve conflicts: combine RadioLib preamble/watchdog fields; keep kiss_modem and MQTT envs.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -100,6 +100,14 @@ Here are some general principals you should try to adhere to:
 
 Help us prioritize! Please react with thumbs-up to issues/PRs you care about most. We look at reaction counts when planning work.
 
+### Running unit tests
+
+To run unit tests, run the following command:
+
+```bash
+pio test --environment native --verbose
+```
+
 ## Road-Map / To-Do
 
 There are a number of fairly major features in the pipeline, with no particular time-frames attached yet. In very rough chronological order:
@@ -119,4 +127,4 @@ There are a number of fairly major features in the pipeline, with no particular
 
 - Report bugs and request features on the [GitHub Issues](https://github.com/ripplebiz/MeshCore/issues) page.
 - Find additional guides and components on [my site](https://buymeacoffee.com/ripplebiz).
-- Join [MeshCore Discord](https://discord.gg/BMwCtwHj5V) to chat with the developers and get help from the community.
+- Join [MeshCore Discord](https://meshcore.gg) to chat with the developers and get help from the community.