Anomaly detection on ESP32 with 24 bytes of RAM — no cloud, no malloc

The core idea: Welford's online algorithm The standard way to compute mean and standard deviation requires storing all samples first, then doing two passes. That's fine in Python. On a microcontroller with 320 KB of RAM, it's a non-starter. John Welford solved this in 1962. His algorithm maintains a running mean and variance in a single pass, using only three values: typedef struct { uint32_t count ; // samples processed float mean ; // running mean float M2 ; // sum of squared deviations from m