add waveshare esp32-c6 sx1262 variant (no lr1121)

[aslater3]

Summary

This PR adds a new Waveshare ESP32-C6 (SX1262) board variant with display support, while intentionally excluding LR1121-specific logic/wiring.

The goal is to provide an upstream-safe, buildable Waveshare C6 target without introducing custom external-radio assumptions.

What’s Included

• New variant: variants/waveshare_esp32_c6/
• Board class:
  • variants/waveshare_esp32_c6/WaveshareESP32C6Board.h
• Display driver for the ESP32-C6-LCD-1.47 form factor:
  • variants/waveshare_esp32_c6/WaveshareESP32C6LCDDisplay.h
  • variants/waveshare_esp32_c6/WaveshareESP32C6LCDDisplay.cpp
• Variant target wiring/runtime glue:
  • variants/waveshare_esp32_c6/target.h
  • variants/waveshare_esp32_c6/target.cpp
• Variant build environments:
  • variants/waveshare_esp32_c6/platformio.ini
  • env:Waveshare_ESP32_C6_repeater_
  • env:Waveshare_ESP32_C6_room_server_
  • env:Waveshare_ESP32_C6_companion_radio_ble_

Scope / Non-Goals

• No LR1121 support in this PR.
• No LR1121 wrappers or dual-band TX-power handling in this PR.
• No custom-wired external radio profiles added to upstream variants.

Notes

• Radio path in this PR uses the existing SX1262 stack (CustomSX1262 + CustomSX1262Wrapper) with variant-local pin mapping.
• Display scaling/offset macros are exposed in variant flags to account for panel geometry/corner clipping.

Validation

• PlatformIO recognizes all new Waveshare_ESP32_C6_* environments.