Fix Heltec V3 LoRa reset pin

[robekl]

Summary

• set P_LORA_RESET to 12 for the Heltec V3 variant
• align the SX1262 reset wiring with Heltec's published V3 board mapping
• leave the rest of the Heltec V3 configuration unchanged

Why this is the right fix

Heltec's WiFi LoRa 32 V3 pin map and datasheet both document the SX1262 reset line on GPIO12 as LoRa_RST. MeshCore already passes P_LORA_RESET into the Heltec V3 radio Module constructor, so defining that pin as disconnected was inconsistent with the published hardware wiring.

Setting P_LORA_RESET to 12 matches the vendor mapping already used by the closely related Heltec V4 variant and corrects the V3 board definition without changing any other board behavior.

Authoritative sources:

• Heltec WiFi LoRa 32 V3 pin map: https://resource.heltec.cn/download/WiFi_LoRa_32_V3/Wi-Fi_LoRa32_V3.2_Pinmap.png
• Heltec WiFi LoRa 32 V3 datasheet: https://resource.heltec.cn/download/WiFi_LoRa_32_V3/HTIT-WB32LA_V3%28Rev1.1%29.pdf

Validation

• built Heltec_v3_repeater successfully after the pin correction
• reviewed the repo for other Heltec V3 files that encode the reset pin and did not find additional board-specific references that needed updating

[robekl]

Looking through the history, this also seems justified.

The incorrect value was introduced in c4a2b139 ("moved HeltecV3Board.h to variant folder"), where variants/heltec_v3/platformio.ini gained an explicit P_LORA_RESET=RADIOLIB_NC while the rest of the SX1262 pin block was already the documented Heltec layout (DIO1=14, NSS=8, BUSY=13, SCK=9, MISO=11, MOSI=10). I checked the subsequent history and did not find any commit or PR discussion explaining why V3 should intentionally ignore a wired reset line.

That makes this PR look like a straightforward board-definition correction. Heltec's published WiFi LoRa 32 V3 pin map and datasheet show LoRa_RST on GPIO12, and the target code already passes P_LORA_RESET into the SX1262 Module constructor, so using 12 here is consistent with both the vendor docs and the existing driver wiring.

Authoritative sources:

• https://resource.heltec.cn/download/WiFi_LoRa_32_V3/Wi-Fi_LoRa32_V3.2_Pinmap.png
• https://resource.heltec.cn/download/WiFi_LoRa_32_V3/HTIT-WB32LA_V3%28Rev1.1%29.pdf