feat(boards): LilyGo T-Beam S3 Supreme support

ESP32-S3 + SX1262 + SH1106 OLED + AXP2101 PMIC, native USB-C.

The AXP2101 PMIC gates power to the LoRa chip and the OLED. Without
its init sequence (ALDO3 = 3.3 V for LoRa, ALDO1 = 3.3 V for OLED)
the SX1262 never responds on SPI and radio init fails.

Pin map verified against MeshCore's variants/lilygo_tbeam_supreme_SX1262.
PMIC lives on a dedicated I²C1 bus (SDA=42, SCL=41) separate from the
SH1106 on I²C0 (SDA=17, SCL=18); I²C1 is used blocking for a one-shot
init and then dropped. TCXO at 1.6 V via DIO3.

New src/driver/axp.rs holds the AXP2101 init sequence — kept minimal
(only the LoRa + OLED rails), since DongLoRa is a LoRa-over-USB bridge
and every other rail (GPS, BME280, IMU, SD, batt ADC) is out of scope.

src/driver/axp.rs

@@ -0,0 +1,64 @@
+//! AXP PMIC init — turn on the rails that feed LoRa and the OLED.
+//!
+//! T-Beam–class boards gate LoRa, OLED (and GPS/sensors, which this firmware
+//! does not use) through an X-Powers PMIC on I²C. Until the PMIC is told to
+//! enable the right LDOs/DCDCs, the SX126x/SX127x chip sits unpowered and
+//! `LoRa::new` fails. This module's only job is to flip those switches.
+//!
+//! Two PMICs are covered:
+//!
+//! * [`axp2101_init_lora_oled`] — LilyGo T-Beam S3 Supreme. ALDO3 = 3.3 V
+//!   feeds the SX1262; ALDO1 = 3.3 V feeds the SH1106 OLED. Both live on a
+//!   dedicated I²C1 bus (separate from the display).
+//! * [`axp192_init_lora_oled`] — LilyGo T-Beam (classic). LDO2 = 3.3 V feeds
+//!   the SX1276; DCDC1 = 3.3 V feeds the SSD1306 OLED. PMIC shares the
+//!   display I²C bus.
+//!
+//! Everything unrelated to LoRa + OLED (GPS, sensors, SD, batt ADC) is left
+//! alone. Out-of-scope for a transparent LoRa-over-USB bridge.
+//!
+//! Init is blocking on purpose. It runs once during `into_parts`, which is a
+//! synchronous function called before task spawning. Using the blocking
+//! `embedded_hal` trait keeps the PMIC wiring out of the async machinery and
+//! lets the caller drop the I²C bus immediately after init (no bus handoff).
+
+use embedded_hal::i2c::I2c;
+
+/// Both chips respond at this 7-bit I²C address.
+const PMIC_ADDR: u8 = 0x34;
+
+// ── AXP2101 (T-Beam S3 Supreme) ──────────────────────────────────────
+
+/// LDO on/off control register. Bits:
+///   0 = ALDO1, 1 = ALDO2, 2 = ALDO3, 3 = ALDO4, 4 = BLDO1, 5 = BLDO2.
+const AXP2101_REG_LDO_ONOFF: u8 = 0x90;
+/// ALDO1 voltage register (OLED rail on T-Beam Supreme).
+const AXP2101_REG_ALDO1_V: u8 = 0x92;
+/// ALDO3 voltage register (LoRa rail on T-Beam Supreme).
+const AXP2101_REG_ALDO3_V: u8 = 0x94;
+
+/// Voltage code for 3.3 V on ALDOx: 0.5 V + 28 × 100 mV.
+const AXP2101_V_3V3: u8 = 28;
+
+/// Mask enabling ALDO1 + ALDO3 in [`AXP2101_REG_LDO_ONOFF`].
+const AXP2101_ALDO1_ALDO3: u8 = 0b0000_0101;
+
+/// Bring up LoRa (ALDO3) and OLED (ALDO1) rails at 3.3 V.
+///
+/// Voltage registers are set before the enable bits to avoid glitching the
+/// rails through the reset-default voltage. Other rails are left untouched
+/// (read-modify-write on the enable register) so any board-specific OTP
+/// defaults stay intact.
+pub fn axp2101_init_lora_oled<I: I2c>(i2c: &mut I) -> Result<(), I::Error> {
+    i2c.write(PMIC_ADDR, &[AXP2101_REG_ALDO3_V, AXP2101_V_3V3])?;
+    i2c.write(PMIC_ADDR, &[AXP2101_REG_ALDO1_V, AXP2101_V_3V3])?;
+
+    let mut onoff = [0u8; 1];
+    i2c.write_read(PMIC_ADDR, &[AXP2101_REG_LDO_ONOFF], &mut onoff)?;
+    i2c.write(
+        PMIC_ADDR,
+        &[AXP2101_REG_LDO_ONOFF, onoff[0] | AXP2101_ALDO1_ALDO3],
+    )?;
+
+    Ok(())
+}

src/driver/mod.rs

@@ -1,11 +1,19 @@
-#[cfg(any(feature = "wio_tracker_l1", feature = "elecrow_thinknode_m2"))]
+#[cfg(any(
+    feature = "wio_tracker_l1",
+    feature = "elecrow_thinknode_m2",
+    feature = "lilygo_tbeam_supreme"
+))]
 pub mod sh1106;
 
+#[cfg(feature = "lilygo_tbeam_supreme")]
+pub mod axp;
+
 #[cfg(any(
     feature = "heltec_v3",
     feature = "heltec_v3_uart",
     feature = "heltec_v4",
     feature = "elecrow_thinknode_m2",
+    feature = "lilygo_tbeam_supreme",
     feature = "wio_tracker_l1",
     feature = "waveshare_rp2040_lora"
 ))]
@@ -51,7 +59,11 @@ where
     }
 }
 
-#[cfg(any(feature = "wio_tracker_l1", feature = "elecrow_thinknode_m2"))]
+#[cfg(any(
+    feature = "wio_tracker_l1",
+    feature = "elecrow_thinknode_m2",
+    feature = "lilygo_tbeam_supreme"
+))]
 impl<I> DisplayBrightness for sh1106::Sh1106<I>
 where
     I: embedded_hal_async::i2c::I2c,