Enhance buzzer detection logic to group intermittent matches with a 500 ms quiet tail, updating relevant configurations and documentation.

main/processing.h

@@ -14,6 +14,7 @@ typedef struct {
     det_state_t state;
     uint32_t triggers;
     uint32_t last_trigger_s;  // uptime seconds of the last trigger, 0 = never
+    uint32_t last_buzz_ms;    // detected duration, excluding final quiet tail
 } proc_stats_t;
 
 esp_err_t processing_start(void);