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>

pubspec.lock

@@ -130,6 +130,11 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_web_plugins:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   glob:
     dependency: transitive
     description:
@@ -418,6 +423,62 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.6.0"
+  shared_preferences:
+    dependency: "direct main"
+    description:
+      name: shared_preferences
+      sha256: c3025c5534b01739267eb7d76959bbc25a6d10f6988e1c2a3036940133dd10bf
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.5.5"
+  shared_preferences_android:
+    dependency: transitive
+    description:
+      name: shared_preferences_android
+      sha256: e8d4762b1e2e8578fc4d0fd548cebf24afd24f49719c08974df92834565e2c53
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.23"
+  shared_preferences_foundation:
+    dependency: transitive
+    description:
+      name: shared_preferences_foundation
+      sha256: "4e7eaffc2b17ba398759f1151415869a34771ba11ebbccd1b0145472a619a64f"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.5.6"
+  shared_preferences_linux:
+    dependency: transitive
+    description:
+      name: shared_preferences_linux
+      sha256: "580abfd40f415611503cae30adf626e6656dfb2f0cee8f465ece7b6defb40f2f"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.1"
+  shared_preferences_platform_interface:
+    dependency: transitive
+    description:
+      name: shared_preferences_platform_interface
+      sha256: "649dc798a33931919ea356c4305c2d1f81619ea6e92244070b520187b5140ef9"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.2"
+  shared_preferences_web:
+    dependency: transitive
+    description:
+      name: shared_preferences_web
+      sha256: c49bd060261c9a3f0ff445892695d6212ff603ef3115edbb448509d407600019
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.3"
+  shared_preferences_windows:
+    dependency: transitive
+    description:
+      name: shared_preferences_windows
+      sha256: "94ef0f72b2d71bc3e700e025db3710911bd51a71cefb65cc609dd0d9a982e3c1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.4.1"
   shelf:
     dependency: transitive
     description: