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

justfile

@@ -10,6 +10,7 @@ heltec_v3      := "heltec_v3 xtensa-esp32s3-none-elf esp32s3"
 heltec_v3_uart := "heltec_v3_uart xtensa-esp32s3-none-elf esp32s3"
 heltec_v4      := "heltec_v4 xtensa-esp32s3-none-elf esp32s3"
 elecrow_thinknode_m2 := "elecrow_thinknode_m2 xtensa-esp32s3-none-elf esp32s3"
+lilygo_tbeam         := "lilygo_tbeam xtensa-esp32-none-elf esp32"
 lilygo_tbeam_supreme := "lilygo_tbeam_supreme xtensa-esp32s3-none-elf esp32s3"
 rak_wisblock_4631  := "rak_wisblock_4631 thumbv7em-none-eabihf nRF52840_xxAA"
 wio_tracker_l1     := "wio_tracker_l1 thumbv7em-none-eabihf nRF52840_xxAA"
@@ -19,7 +20,7 @@ builds_dir := "builds"
 version := `sed -n 's/^version = "\(.*\)"/\1/p' Cargo.toml`
 
 # All known boards
-boards := "heltec_v3 heltec_v3_uart heltec_v4 elecrow_thinknode_m2 lilygo_tbeam_supreme rak_wisblock_4631 waveshare_rp2040_lora wio_tracker_l1"
+boards := "heltec_v3 heltec_v3_uart heltec_v4 elecrow_thinknode_m2 lilygo_tbeam lilygo_tbeam_supreme rak_wisblock_4631 waveshare_rp2040_lora wio_tracker_l1"
 
 # Install all required tools and toolchains
 setup:
@@ -215,6 +216,7 @@ _info name:
      elif [ "{{name}}" == "heltec_v3_uart" ]; then echo "{{heltec_v3_uart}}"; \
      elif [ "{{name}}" == "heltec_v4" ]; then echo "{{heltec_v4}}"; \
      elif [ "{{name}}" == "elecrow_thinknode_m2" ]; then echo "{{elecrow_thinknode_m2}}"; \
+     elif [ "{{name}}" == "lilygo_tbeam" ]; then echo "{{lilygo_tbeam}}"; \
      elif [ "{{name}}" == "lilygo_tbeam_supreme" ]; then echo "{{lilygo_tbeam_supreme}}"; \
      elif [ "{{name}}" == "rak_wisblock_4631" ]; then echo "{{rak_wisblock_4631}}"; \
      elif [ "{{name}}" == "waveshare_rp2040_lora" ]; then echo "{{waveshare_rp2040_lora}}"; \