feat(radio): honest TX power for GAT562 30S external PA

gat562_30s_mesh_kit has an always-on external PA rated at +30dBm, but the
firmware wrote tx_power_dbm straight to the SX1262 register (capped at 22),
so the app/CLI/UI never matched the real radiated power and couldn't ask
for more than 22 even though the hardware supports it.

Add a generic, macro-gated PA gain-curve resolution in
RadioLibWrapper::setTxPower() (the single choke point every TX-power path
already funnels through), reusable by any future board with a similar PA.
For this board, reuse the vendor-measured 869MHz curve from the open
upstream Meshtastic PR that added it for the same physical module
(meshtastic/firmware#11212): pick the lowest SX1262 setting whose measured
output reaches the requested dBm, clamped at the PA's saturation knee.
Bump LORA_TX_POWER/MAX_LORA_TX_POWER to 30 for this variant only -- the
other three GAT562 boards use the SX1262's own PA_BOOST (22dBm, no
external PA) and are unaffected.

Since a request below the PA's floor gain (14dBm) still radiates at that
floor, also make CommonCLICallbacks::setTxPower() return what was actually
applied, and have every setter (BLE CMD_SET_RADIO_TX_POWER, CLI "tx",
simple_repeater/room_server/sensor) persist and report that value instead
of the raw request -- so tx_power_dbm never silently disagrees with the
physical output in either direction.

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

examples/simple_sensor/SensorMesh.cpp

@@ -848,8 +848,9 @@ void SensorMesh::updateFloodAdvertTimer() {
   }
 }
 
-void SensorMesh::setTxPower(int8_t power_dbm) {
+int8_t SensorMesh::setTxPower(int8_t power_dbm) {
   radio_driver.setTxPower(power_dbm);
+  return radio_driver.getTxPower();
 }
 
 void SensorMesh::formatStatsReply(char *reply) {

examples/simple_sensor/SensorMesh.h

@@ -67,7 +67,7 @@ public:
   void setLoggingOn(bool enable) override {  }
   void eraseLogFile() override { }
   void dumpLogFile() override { }
-  void setTxPower(int8_t power_dbm) override;
+  int8_t setTxPower(int8_t power_dbm) override;
   void formatNeighborsReply(char *reply) override {
     strcpy(reply, "not supported");
   }