ESP32-S3 WiFi CSI运动检测固件

Write me an ESP32-S3 firmware that captures WiFi CSI data and detects movement in a room. Requirements: Connect to my home WiFi as a passive client Capture CSI packets continuously Calculate the variance of CSI amplitude over a 2-second window When variance exceeds a threshold, mark the state as "motion detected" When it drops below, mark as "still" Output JSON over serial: timestamp, state, variance_value Use the official esp_wifi.h CSI API. Add comments explaining each section so I can tune the threshold later.