feat(boards): LilyGo T-Beam (classic) support

First classic-ESP32 (non-S3) board in the firmware, and first SX127x
radio. ESP32 + SX1276 + SSD1306 OLED + AXP192 PMIC, CP2102 USB-UART
bridge. Pin map verified from MeshCore variants/lilygo_tbeam_SX1276.

The AXP192 gates power to the LoRa chip and OLED. Its I²C bus is
shared with the display, so the firmware builds I²C0 in blocking mode
first for the PMIC init, then converts the same handle to async and
hands it to the display task — avoids double-consuming the peripheral.

Lora-phy's Sx127x support drives DIO0 as the sole IRQ (SX127x has no
BUSY line); the chip runs from a crystal, tx_boost routes +20 dBm
through PA_BOOST.

The `esp-hal` / `esp-rtos` / `esp-backtrace` / `esp-println` deps have
been restructured so the chip flavour (esp32 vs esp32s3) is selected
at the per-board feature level instead of baked into the dep lines.
This keeps the existing S3 boards building on esp32s3 while the new
T-Beam feature selects classic esp32 via the same dependency set.

LoRaBoard gains supported_sf_bitmap() / supported_bw_bitmap() methods
(with SX126x defaults) so the T-Beam can report SF6–SF12 via GET_INFO
— the SX1276 has no SF5. radio_chip_id() reports 0x0011 per
donglora-protocol RadioChipId::Sx1276. freq_range_hz widens to the
SX1276 datasheet span of 137 MHz–1020 MHz.

New modules:
- src/hal/esp32.rs           — classic-ESP32 MCU primitives
- src/board/esp32.rs         — Sx127x radio + SSD1306 display pipe
- src/board/lilygo_tbeam.rs  — the board file
- src/driver/axp.rs          — AXP192 init added alongside AXP2101

src/driver/mod.rs

@@ -5,7 +5,7 @@
 ))]
 pub mod sh1106;
 
-#[cfg(feature = "lilygo_tbeam_supreme")]
+#[cfg(any(feature = "lilygo_tbeam_supreme", feature = "lilygo_tbeam"))]
 pub mod axp;
 
 #[cfg(any(
@@ -14,6 +14,7 @@ pub mod axp;
     feature = "heltec_v4",
     feature = "elecrow_thinknode_m2",
     feature = "lilygo_tbeam_supreme",
+    feature = "lilygo_tbeam",
     feature = "wio_tracker_l1",
     feature = "waveshare_rp2040_lora"
 ))]