Fix blank OLED on T-Beam Supreme V3 (I2C bus + 0x3D address)

The SH1106 OLED on the LilyGo T-Beam Supreme V3 never lights up because:

1. The primary I2C bus (Wire) that the OLED, BME280 and magnetometer share
   is never initialized. The PMU/RTC use Wire1 (via XPowersLib); nothing
   brings up Wire on PIN_BOARD_SDA/PIN_BOARD_SCL, so the display driver
   talks on the wrong default pins.
2. The OLED is at I2C address 0x3D on this board (0x3C is taken by the
   QMC6310 magnetometer), but SH1106Display::begin() only tried 0x3C.

Initialize Wire for TBEAM_SUPREME_SX1262, and have SH1106Display::begin()
prefer 0x3D (only ever used by the OLED) before falling back to 0x3C.
Backwards-compatible for boards with the OLED at 0x3C.

Closes #2609

src/helpers/esp32/TBeamBoard.cpp

@@ -16,6 +16,16 @@ void TBeamBoard::begin() {
     
     ESP32Board::begin();
 
+#ifdef TBEAM_SUPREME_SX1262
+    // On the T-Beam S3 Supreme the PMU + RTC sit on Wire1 (GPIO 42/41, brought
+    // up by XPowersLib), while the SH1106 OLED and the BME280/QMC6310 sensors
+    // sit on the primary bus, Wire (GPIO PIN_BOARD_SDA/PIN_BOARD_SCL). Nothing
+    // else initialises Wire on this board, so the display driver would
+    // otherwise talk on the wrong (default) pins and display.begin() fails,
+    // leaving the screen blank. Bring the OLED bus up here.
+    Wire.begin(PIN_BOARD_SDA, PIN_BOARD_SCL);
+#endif
+
     power_init();
 
     //Configure user button

src/helpers/ui/SH1106Display.cpp

@@ -11,7 +11,17 @@ bool SH1106Display::i2c_probe(TwoWire &wire, uint8_t addr)
 
 bool SH1106Display::begin()
 {
-  return display.begin(DISPLAY_ADDRESS, true) && i2c_probe(Wire, DISPLAY_ADDRESS);
+  // Address selection: on some board revisions (notably the LilyGo T-Beam
+  // Supreme V3) the OLED lives at 0x3D because 0x3C is occupied by a
+  // magnetometer (QMC6310N). 0x3D is only ever used by the OLED, so prefer it
+  // when present, otherwise fall back to the standard 0x3C (DISPLAY_ADDRESS).
+  uint8_t addr = 0;
+  if (i2c_probe(Wire, 0x3D)) {
+    addr = 0x3D;
+  } else if (i2c_probe(Wire, DISPLAY_ADDRESS)) {
+    addr = DISPLAY_ADDRESS;
+  }
+  return addr && display.begin(addr, true);
 }
 
 void SH1106Display::turnOn()