merge: upstream/dev into observer-firmware-dev

Brings in the external FEM gain preferences (fem_txgain, PR #3137 plus the
companion-side port), the AGC reset rxgain fix, the LR2021 preamble/IRQ
timeout logic, and assorted variant fixes (T096, T-Echo Card TCXO, promicro
pinmap, minewsemi, R1 Neo).

Conflict resolutions:

- SH1106Display: both sides fixed T-Beam Supreme startup independently. Kept
  our _initialized guard and DISPLAY_ADDRESS_ALT override, took upstream's
  SA0-pair fallback and its unconditional display.begin() so the frame buffer
  is allocated even when no panel answers.
- MyMesh/SensorMesh/CommonCLI: took upstream's fem_txgain default and wiring,
  kept our comments and the observer-side prefs layout.

Also fixes CustomLLCC68Wrapper, which upstream missed when sx126xResetAGC
gained its rx_boost_gain parameter. No variant builds that wrapper today, so
neither tree failed to compile.

examples/simple_sensor/SensorMesh.cpp

@@ -737,6 +737,7 @@ SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::Millise
   _prefs.gps_interval = 0;
   _prefs.advert_loc_policy = ADVERT_LOC_PREFS;
   _prefs.radio_fem_rxgain = 1;
+  _prefs.radio_fem_txgain = 0;
 
   memset(default_scope.key, 0, sizeof(default_scope.key));
 }
@@ -773,6 +774,7 @@ void SensorMesh::begin(FILESYSTEM* fs) {
   radio_driver.setParams(_prefs.freq, _prefs.bw, _prefs.sf, _prefs.cr);
   radio_driver.setTxPower(_prefs.tx_power_dbm);
   board.setLoRaFemLnaEnabled(_prefs.radio_fem_rxgain);   // LoRa FEM LNA (FEM boards only)
+  board.setLoRaFemPaGainEnabled(_prefs.radio_fem_txgain);
 
   updateAdvertTimer();
   updateFloodAdvertTimer();