Add Elecrow ThinkNode G3 room server variant

[lowclearance]

Add Elecrow ThinkNode G3 (ESP32-S3 + SX1262)

Adds an unofficial variant for the Elecrow ThinkNode G3, model ILM13103D. It is an ESP32-S3-WROOM-1-N8R8 with an LR1262 module (SX1262, TCXO, RF switch) and a CH340 USB-UART. No display, no GPS, no battery, USB-powered. This is not the ThinkNode M7: the M7 is an LR1110 on a different PCB, and its pins must not be reused here.

Elecrow has not published a schematic. The radio map was recovered from a stock US915 firmware dump by nsbradley88 (Meshtastic discussion #9434, 23 Sep 2026) and matches the earlier pad probe. With the TCXO at 3.0 V, a room-server build on one US915 unit advertised, was heard by several other nodes, and accepted a post from another node.

Pins

Signal | GPIO -- | -- NSS / SCK / MOSI / MISO | 39 / 42 / 40 / 41 RESET | 21 BUSY | 47 DIO1 | 15 Antenna switch / PE_EN | 45, driven high at init TCXO on DIO3 | 3.0 V, radio-controlled Reload button | 4 LINK LED | 5, unused LoRa LED | 6, active-low

DIO2 is the RF switch. Flash is 8 MB, PSRAM is 8 MB octal. qio_opi is required. A DIO build boots and reports PSRAM ID read error: 0x00ffffff.

The CH340 has no auto-reset wiring. Upload uses --before=no-reset at 115200. Download mode is hold BOOT, tap RESET, release BOOT while the uploader is already waiting on the port. The console is the CH340, not the ESP32-S3 native USB port.

Roles

• ThinkNode_G3_room_server is tested on hardware.
• ThinkNode_G3_repeater compiles, but it was not the image run on air.
• ThinkNode_G3_companion_radio_ble and ThinkNode_G3_companion_radio_usb compile, but they were not run on air.

Ethernet is omitted. The onboard PHY is a CH390, and its SPI pins are not confirmed. The M7 Ethernet map uses GPIO 47, which is BUSY on this board. Wi-Fi is omitted for the same reason: this PR is the radio variant only.

Tested

One US915 G3, room-server firmware:

• The boot log no longer reports a PSRAM ID error.
• An advert was heard by multiple existing nodes.
• A post from another node was accepted.
• The blue LoRa LED is off at idle and on only during transmit.

Not tested: repeater forwarding, companion BLE or USB, Ethernet, Wi-Fi, and any 868 MHz unit.