fix(stalker): fence stale portal modes

.changes/stalker-smart-discovery.md

@@ -6,4 +6,5 @@ area: stalker
 Stalker setup now accepts a host or `/c` address, discovers the working API
 endpoint and authentication mode, and rechecks connection details edited
 later. Canceled or failed edits leave the saved playlist and active session
-unchanged.
+unchanged. Completed edits reject requests still holding the previous portal
+mode.