disabled share_instance for reliable announces

With share_instance = Yes, announces weren't being sent over TCP
in Docker environments. Setting it to No ensures each TinyWeb
instance manages its own Reticulum interfaces directly.

app.py

@@ -53,7 +53,7 @@ def ensure_rns_config(config_dir):
     with open(config_file, "w") as f:
         f.write(f"""[reticulum]
   enable_transport = False
-  share_instance = Yes
+  share_instance = No
 
 [logging]
   loglevel = 4