fix: primary session timeout not tracking RPC activity

The primary session inactivity timeout was only tracking HID-related
activity (keyboard, mouse, mass storage) but not general RPC messages.
This meant users watching video or interacting with the UI would be
timed out even though they were actively using the session.

Added UpdateLastActive call in onRPCMessage to track any valid RPC
activity, ensuring all user interactions reset the inactivity timer.

jsonrpc.go

@@ -179,6 +179,9 @@ func onRPCMessage(message webrtc.DataChannelMessage, session *Session) {
 		return
 	}
 
+	// Update last active timestamp for any valid RPC activity
+	sessionManager.UpdateLastActive(session.ID)
+
 	var request JSONRPCRequest
 	err := json.Unmarshal(message.Data, &request)
 	if err != nil {