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/app/reload.h

@@ -7,8 +7,9 @@ int handle_reload(const char *user_cfg_path,
                   char *current_config_path, char *current_sound_dir,
                   char *current_mouse_config_path, char *current_mouse_sound_dir,
                   int current_mute, int current_verbose,
-                  int current_mouse_volume_arg, int current_keyboard_mute,
-                  int current_mouse_mute, int *current_keyboard_enabled, int *current_mouse_enabled);
+                  int current_keyboard_mute, int current_mouse_mute,
+                  int *current_keyboard_enabled, int *current_mouse_enabled,
+                  int *current_system_volume_following);
 
 #endif // VBX_RELOAD_H