feat: add settings mgmt and split debug transport snippets

firmware/libs/settings_mgmt/include/settings_mgmt.h

@@ -0,0 +1,34 @@
+#ifndef SETTINGS_MGMT_H
+#define SETTINGS_MGMT_H
+
+#include <zephyr/types.h>
+
+struct app_settings_t {
+    /* System */
+    char dev_name[33];
+    
+    /* Audio */
+    uint8_t vol;
+    uint8_t shuffle_mode; /* 0: Rnd, 1: No-Rep */
+
+    /* BLE */
+    uint32_t ble_timeout;  /* Seconds, 0xFFFFFFFF = forever */
+    uint16_t ble_interval; /* Milliseconds */
+
+    /* Power & Calibration */
+    uint8_t chg_mode;      /* 0: 500mA, 1: 1A, 2: Auto */
+    uint16_t off_threshold;/* mV */
+    int16_t adc_gain;
+    int16_t adc_offset;
+};
+
+/* Global access to the current runtime configuration */
+extern struct app_settings_t app_cfg;
+
+/* Initializes the settings subsystem and loads values from flash */
+int settings_mgmt_init(void);
+
+/* Sets a setting via string path (for your protocol) */
+int settings_mgmt_set_by_path(const char *path, const void *value, size_t len);
+
+#endif