feat(src/daemon): set LAPCTL_DAEMON_INTERNAL env var internally

Set an internal environment variable when the daemon starts to allow components to detect internal mode and prepare for future runtime configuration.

- New Features
  - Introduce `LAPCTL_DAEMON_INTERNAL` set to "1" inside the daemon.
- Enhancements
  - Enable downstream components to detect internal daemon execution.

src/daemon/mod.rs

@@ -6,6 +6,9 @@ mod dbus_iface;
 
 pub async fn run() -> Result<(), Box<dyn Error>> {
     info!("Starting lapctld daemon...");
+    unsafe {
+        std::env::set_var("LAPCTL_DAEMON_INTERNAL", "1");
+    }
     let _connection = Builder::system()?
         .name("org.lapctl")?
         .serve_at("/org/lapctl", dbus_iface::LapctlInterface::default())?