Make progress bar cursor draggable

controller.py

@@ -418,6 +418,13 @@ class Controller:
             return None
         return self.zidoo.now_playing()
 
+    def zidoo_seek(self, position_ms: int):
+        """Jump the Zidoo's film -- the AVR card's now-playing -- to
+        position_ms."""
+        if not self.zidoo:
+            raise TargetError("No Zidoo is configured to seek in")
+        self.zidoo.seek(position_ms)
+
     # -- one snapshot for the UI ------------------------------------------
     def state(self) -> dict:
         snapshot = {