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/instance/console_windows.go

@@ -0,0 +1,37 @@
+//go:build windows
+
+package instance
+
+import (
+	"os"
+	"syscall"
+)
+
+var (
+	kernel32        = syscall.NewLazyDLL("kernel32.dll")
+	procFreeConsole = kernel32.NewProc("FreeConsole")
+	user32          = syscall.NewLazyDLL("user32.dll")
+	procShowWindow  = user32.NewProc("ShowWindow")
+)
+
+const swHide = 0
+
+// HideConsole hides any console window and detaches from it.
+func HideConsole() {
+	hwnd, _, _ := kernel32.NewProc("GetConsoleWindow").Call()
+	if hwnd != 0 {
+		_, _, _ = procShowWindow.Call(hwnd, swHide)
+	}
+	_, _, _ = procFreeConsole.Call()
+	redirectStdioToNul()
+}
+
+func redirectStdioToNul() {
+	nul, err := os.OpenFile("NUL", os.O_RDWR, 0)
+	if err != nil {
+		return
+	}
+	os.Stdin = nul
+	os.Stdout = nul
+	os.Stderr = nul
+}