Phase 7: EC11 encoder, life counter views, WS2812B RMT + LEDC buzzer feedback, E2E UI state machine; document build/hardware notes

main/buzzer.h

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+/*
+ * MTG RFID Companion - Piezo buzzer driver (LEDC PWM)
+ *
+ * Phase 7 Step 7.4: Subtle audio cues on GPIO 14.
+ */
+
+#pragma once
+
+#include "esp_err.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Initialize LEDC PWM channel for the buzzer.
+ */
+esp_err_t buzzer_init(void);
+
+/**
+ * @brief Start a tone at the given frequency.
+ */
+esp_err_t buzzer_start(uint32_t freq_hz, uint32_t duty_percent);
+
+/**
+ * @brief Silence the buzzer.
+ */
+esp_err_t buzzer_stop(void);
+
+/**
+ * @brief Play a short chirp (blocking).
+ * @param freq_hz Tone frequency
+ * @param duration_ms Tone length in ms
+ */
+esp_err_t buzzer_chirp(uint32_t freq_hz, uint32_t duration_ms);
+
+#ifdef __cplusplus
+}
+#endif