refactor(app): Material from material_ui instead of the SDK

Flutter 3.47 moved Material and Cupertino out of the SDK into material_ui and cupertino_ui, which ship weekly. The SDK imports are deprecated from the November 2026 stable release and removed in 2027, and the strict pre-push check would block every push then. The app's one Material import now comes from material_ui ^1.5.0, so everything built from here on uses the new import.

Packages that still import package:flutter/material.dart (Serverpod's Flutter packages, later the rich-text editor) see the app's theme and localizations only through MaterialUiCompatibilityBridge, set in MaterialApp.builder. The bridge is deprecated on purpose, as a reminder to remove it, so its use carries a documented ignore until those packages have moved.

google_fonts is removed: it was unused, and by default it downloads fonts from Google at runtime, which sends every user's IP address to Google.

AGENTS.md: Material comes from material_ui.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/pubspec.yaml

@@ -29,9 +29,9 @@ dependencies:
   cupertino_icons: ^1.0.5
   flutter:
     sdk: flutter
-  google_fonts: ^8.1.0
   halkyon_learn_client:
     path: ../halkyon_learn_client
+  material_ui: ^1.5.0
   serverpod_auth_idp_flutter: 4.0.2
   serverpod_flutter: 4.0.2