fix(webconfig): persist the admin password before completing Ethernet onboarding

The upstream `password` command saves /prefs.json without reporting the
result, and WebConfig overwrites its reply with "OK". If that write failed
while the later /mqtt.json write succeeded, wifi.setup_complete was set and
the factory password came back after reboot with first-run setup
suppressed. onInitialSetupComplete() now re-saves /prefs.json and records
completion only when it succeeds; otherwise the batch fails, setup stays
open, and no reboot is queued.

examples/simple_repeater/MyMesh.h

@@ -508,6 +508,8 @@ public:
   }
   void onConfigBatchEnd() override;
   bool onInitialSetupComplete() override {
+    // The password command does not report its save; make it durable first.
+    if (!_cli.savePrefs(_fs)) return false;
     MQTTPrefs* obs = _cli.getObserverPrefs();
     obs->network_setup_complete = 1;
     if (_cli.saveObserverPrefs(_fs)) return true;

examples/simple_room_server/MyMesh.h

@@ -498,6 +498,8 @@ public:
   }
   void onConfigBatchEnd() override;
   bool onInitialSetupComplete() override {
+    // The password command does not report its save; make it durable first.
+    if (!_cli.savePrefs(_fs)) return false;
     MQTTPrefs* obs = _cli.getObserverPrefs();
     obs->network_setup_complete = 1;
     if (_cli.saveObserverPrefs(_fs)) return true;