feat(include): add system volume following support

Implement configurable system volume following and replace JSON IPC with binary struct.

- New Feature: Introduce `system_volume_following` CLI and runtime option.
- Enhancement: Extend CLI options, reload, and user‑config APIs to propagate the new flag.
- Enhancement: Add `VbxEvent` binary IPC struct and logging macros for better performance.
- Enhancement: Add helper to persist system volume following state.
- Bug Fix: Remove stale `parse_keyboard_event` prototype.

include/common/ipc.h

@@ -0,0 +1,13 @@
+#ifndef VBX_IPC_H
+#define VBX_IPC_H
+
+#include <stdint.h>
+
+// Lightweight binary structure for IPC between vbx-input and vbx-audio
+// Replaces the heavy JSON parsing
+typedef struct {
+    uint32_t key_code;
+    uint8_t  is_pressed;
+} VbxEvent;
+
+#endif // VBX_IPC_H

include/common/log.h

@@ -0,0 +1,29 @@
+#ifndef VBX_LOG_H
+#define VBX_LOG_H
+
+#include <stdio.h>
+#include <time.h>
+
+// Assuming g_verbose is defined globally or we pass it
+extern int g_verbose;
+extern int is_daemon;
+
+#define LOG_LEVEL_DEBUG 0
+#define LOG_LEVEL_INFO  1
+#define LOG_LEVEL_WARN  2
+#define LOG_LEVEL_ERROR 3
+
+#define LOG_MACRO(level, prefix, out_stream, ...) do { \
+    if (level == LOG_LEVEL_DEBUG && !g_verbose) break; \
+    fprintf(out_stream, "[VBX-%s] ", prefix); \
+    fprintf(out_stream, __VA_ARGS__); \
+    fprintf(out_stream, "\n"); \
+    fflush(out_stream); \
+} while(0)
+
+#define LOG_DEBUG(...) LOG_MACRO(LOG_LEVEL_DEBUG, "DEBUG", stdout, __VA_ARGS__)
+#define LOG_INFO(...)  LOG_MACRO(LOG_LEVEL_INFO,  "INFO",  stdout, __VA_ARGS__)
+#define LOG_WARN(...)  LOG_MACRO(LOG_LEVEL_WARN,  "WARN",  stderr, __VA_ARGS__)
+#define LOG_ERROR(...) LOG_MACRO(LOG_LEVEL_ERROR, "ERROR", stderr, __VA_ARGS__)
+
+#endif // VBX_LOG_H

include/common/utils.h

@@ -29,6 +29,9 @@ void write_runtime_mouse_mute_file(int mute);
 int write_runtime_keyboard_enabled_file(int enabled);
 int write_runtime_mouse_enabled_file(int enabled);
 
+// System volume following helper
+int write_runtime_system_volume_following_file(int enabled);
+
 // Helper functions
 void int_to_str(char *buffer, size_t size, int value);
 char *xstrdup(const char *s);