Adds ESP32-AI-Agent-Skill under Backend & Architecture — the first hardware/embedded systems plugin in this collection.

• GPIO pin validation with safety checks preventing hardware damage
• Code generation for Arduino and ESP-IDF
• 9 ESP32 variants, LVGL UI, 60+ Waveshare boards
• MIT licensed, 50 automated tests

Repo: https://github.com/ezrover/ESP32-AI-Agent-Skill