Add delay before announce to ensure TCP interface is ready

The announce was firing before the TCP transport connection was fully
established, causing Docker instances to never announce over the mesh.

app.py

@@ -93,6 +93,8 @@ def main():
         allow=RNS.Destination.ALLOW_ALL,
     )
 
+    # Brief delay to ensure all interfaces (especially TCP) are fully ready
+    time.sleep(2)
     destination.announce()
     set_setting("dest_hash", destination.hash.hex())
     start_gateway(reticulum)