fix(room_server): support RX boosted gain

The room server never supported RX boosted gain, while the repeater
does. Three consequences on SX1262/SX1268 boards:

- boosted gain was never applied to the radio at boot, so a room server
  ran in power-saving RX mode while an identical repeater ran boosted -
  a real receive-sensitivity difference with nothing pointing at it
- _prefs.rx_boosted_gain was never initialised (the prefs are memset to
  0 before defaults are set), so it defaulted to off
- 'set radio.rxgain on' replied "Error: unsupported" but CommonCLI had
  already written the value to prefs and saved them, so a stale setting
  survived reboot and was never applied

Mirror the repeater's implementation: initialise the pref default under
the same USE_SX1262/USE_SX1268 and SX126X_RX_BOOSTED_GAIN guards, apply
it during radio init, and override setRxBoostedGain() so the CLI reports
success and takes effect.

Built Heltec_v3_room_server (SX1262) and LilyGo_T3S3_sx1276_room_server
(guards compile out cleanly).

examples/simple_room_server/MyMesh.cpp

@@ -658,6 +658,14 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.gps_enabled = 0;
   _prefs.gps_interval = 0;
   _prefs.advert_loc_policy = ADVERT_LOC_PREFS;
+
+#if defined(USE_SX1262) || defined(USE_SX1268)
+#ifdef SX126X_RX_BOOSTED_GAIN
+  _prefs.rx_boosted_gain = SX126X_RX_BOOSTED_GAIN;
+#else
+  _prefs.rx_boosted_gain = 1; // enabled by default;
+#endif
+#endif
   _prefs.radio_fem_rxgain = 1;
 
   next_post_idx = 0;
@@ -700,6 +708,7 @@ void MyMesh::begin(FILESYSTEM *fs) {
 
   radio_driver.setParams(_prefs.freq, _prefs.bw, _prefs.sf, _prefs.cr);
   radio_driver.setTxPower(_prefs.tx_power_dbm);
+  radio_driver.setRxBoostedGainMode(_prefs.rx_boosted_gain);
   board.setLoRaFemLnaEnabled(_prefs.radio_fem_rxgain);
 
   updateAdvertTimer();
@@ -807,6 +816,10 @@ void MyMesh::setTxPower(int8_t power_dbm) {
   radio_driver.setTxPower(power_dbm);
 }
 
+bool MyMesh::setRxBoostedGain(bool enable) {
+  return radio_driver.setRxBoostedGainMode(enable);
+}
+
 void MyMesh::saveIdentity(const mesh::LocalIdentity &new_id) {
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
   IdentityStore store(*_fs, "");

examples/simple_room_server/MyMesh.h

@@ -206,6 +206,7 @@ public:
 
   void dumpLogFile() override;
   void setTxPower(int8_t power_dbm) override;
+  bool setRxBoostedGain(bool enable) override;
 
   void formatNeighborsReply(char *reply) override {
     strcpy(reply, "not supported");