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/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);