refactor: make supervisor internal

src/bin/vibebox-supervisor.rs

@@ -12,6 +12,11 @@ use tracing_subscriber::prelude::*;
 use vibebox::{config, instance, vm, vm_manager};
 
 fn main() -> Result<()> {
+    if env::var("VIBEBOX_INTERNAL").as_deref() != Ok("1") {
+        eprintln!("vibebox-supervisor is internal. Use `vibebox` instead.");
+        std::process::exit(2);
+    }
+
     init_tracing();
     color_eyre::install()?;
 

src/vm_manager.rs

@@ -135,6 +135,7 @@ fn spawn_manager_process(
     if raw_args.len() > 1 {
         cmd.args(&raw_args[1..]);
     }
+    cmd.env("VIBEBOX_INTERNAL", "1");
     if !use_supervisor {
         cmd.env("VIBEBOX_VM_MANAGER", "1");
     }