feat(agent): add crash logs and watchdog startup

- Recover panics to disk for diagnostics
- Add 5-minute watchdog task with startup
- Add -ensure flag to start detached agent
- Add script to pull remote folder via API

lib/instance/ensure.go

@@ -0,0 +1,9 @@
+package instance
+
+// EnsureRunning starts a detached agent if none is holding the mutex.
+func EnsureRunning() error {
+	if AlreadyRunning() {
+		return nil
+	}
+	return Detach()
+}