Rename device identity from DigiRadio to igiRadio

SoftAP SSID, Bluetooth name, and mDNS hostname now use the "igiRadio"
prefix (igiRadio-<serial>, igiradio-<serial>.local), matching the iOS
app's name instead of the firmware project's repo name. Confirmed live:
igiradio-CC4DB4.local resolves, the old digiradio-CC4DB4.local no
longer does.

Also adds the app-side briefs/notes accumulated today (active_source,
volume contract, VU-meter polling, RDS availability) as a single
up-to-date file to hand to Cursor.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Software/components/net/include/net/SoftApConfig.hpp

@@ -41,7 +41,7 @@ public:
      * @brief    setupDefault — factory for the Slice 1 setup SoftAP.
      *
      * @dname    setupDefault
-     * @return   SoftApConfig with SSID DigiRadio-setup.
+     * @return   SoftApConfig with SSID igiRadio-setup.
      * @pubstate none
      *
      * @author   Michele Bigi