feat(ui): hub-endpoint settings dialog with persistence

Studio is no longer hardcoded to localhost:50051. A gear icon
in the sidebar footer opens a small settings dialog where the
operator picks host / port / TLS-on-or-off. Saved values
persist via shared_preferences and Studio reconnects to the
new endpoint immediately.

- data/hub.dart: HubService.loadPersistedEndpoint() called once
  before the first frame; reconnect() persists on every change.
- widgets/fai_settings_dialog.dart: typed form with port range
  validation, live URL preview pill, error surfacing if the
  reconnect fails.
- main.dart: gear icon at the sidebar bottom, replaces the
  static "platform v0.10.42" footer.

shared_preferences added as dependency. flutter analyze clean,
flutter test 2/2, macOS debug build succeeds.

Bumps fai_studio 0.4.0 -> 0.5.0.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

macos/Podfile.lock

@@ -1,15 +1,22 @@
 PODS:
   - FlutterMacOS (1.0.0)
+  - shared_preferences_foundation (0.0.1):
+    - Flutter
+    - FlutterMacOS
 
 DEPENDENCIES:
   - FlutterMacOS (from `Flutter/ephemeral`)
+  - shared_preferences_foundation (from `Flutter/ephemeral/.symlinks/plugins/shared_preferences_foundation/darwin`)
 
 EXTERNAL SOURCES:
   FlutterMacOS:
     :path: Flutter/ephemeral
+  shared_preferences_foundation:
+    :path: Flutter/ephemeral/.symlinks/plugins/shared_preferences_foundation/darwin
 
 SPEC CHECKSUMS:
   FlutterMacOS: d0db08ddef1a9af05a5ec4b724367152bb0500b1
+  shared_preferences_foundation: 7036424c3d8ec98dfe75ff1667cb0cd531ec82bb
 
 PODFILE CHECKSUM: 54d867c82ac51cbd61b565781b9fada492027009