radio: extract CadController and NoiseFloorEstimator, one prefs source

- CadController (stats, window, re-anchor, visits, staircase, safety,
  starvation relax) and NoiseFloorEstimator split out of LoRaRadioBase
  behind a 4-call CadHw interface; Zephyr-free, host unit tests added
- prefs mandatory: setPrefs() before begin(), LoRaConfig fallbacks and the
  companion/observer placeholder prefs removed; LoRaConfig is the one
  defaults source (invalid-prefs fallback now uses the board TX default)
- TX-wait thread stack owned by the base; reconfigureWithParams removed
- driver extension headers on the public include path
  (zephyr/drivers/lora/*.h); patch 0003 include updated
- comment diet (image-identical); rationale moved to devdocs LLD 03

zephcore/src/main_room_server.cpp

@@ -641,7 +641,7 @@ int main(void)
 	 * Dispatcher::begin() → Radio::begin().  Without this, the radio would
 	 * configure on NodePrefs defaults (869.618 MHz) regardless of saved
 	 * settings: CLI readback looked correct but the hardware stayed on EU.
-	 * Mirrors the temp_prefs pattern in main_companion.cpp. */
+	 * Every role binds this way; begin() refuses to start without it. */
 	data_store.loadPrefs(*room_mesh.getNodePrefs());
 	lora_radio.setPrefs(room_mesh.getNodePrefs());