feat: add on-demand device screenshots

driver/base.py

@@ -25,6 +25,15 @@ class Driver(ABC):
     def screenshot(self) -> bytes:
         """Return the current screen as image bytes."""
 
+    def health_check(self) -> None:
+        """Verify the live session without reading the device screen.
+
+        Drivers with a transport-level status endpoint should override this
+        method. The default is a no-op for legacy drivers that do not expose
+        a separate health check.
+        """
+        return None
+
     @abstractmethod
     def tap(self, x: float, y: float) -> None:
         """Tap the screen at the given coordinates."""