feat: adjust app color scheme and text theme

android/app/build.gradle

@@ -45,7 +45,7 @@ android {
         applicationId "com.example.biersommelier"
         // You can update the following values to match your application needs.
         // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
-        minSdkVersion flutter.minSdkVersion
+        minSdkVersion 20
         targetSdkVersion flutter.targetSdkVersion
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName

lib/router/PageRouter.dart

@@ -4,15 +4,44 @@ import 'package:biersommelier/pages/Other.dart';
 import 'package:flutter/material.dart';
 import 'package:go_router/go_router.dart';
 
+// As Flutter does not expose these color types, we have to extend them ourselves
+extension AppColorScheme on ColorScheme {
+  Color get success => const Color(0xFFB4CF67);
+  Color get lightSecondary => const Color(0xFF946C00);
+  Color get hint => const Color(0xFF2187FF);
+  Color get white => const Color(0xFFFFFFFF);
+  Color get black => const Color(0xFF000000);
+}
+
 class PageRouter {
   /// Diese Methode ersetzt router durch die benötigten
   /// Eigenschaften der App (Hintergrundfarbe uä)
   static MaterialApp app() {
     return MaterialApp.router(
       title: 'Biersommelier',
       theme: ThemeData(
-        colorScheme: ColorScheme.fromSeed(seedColor: Colors.transparent),
-        useMaterial3: true,
+        colorScheme: const ColorScheme(
+          primary: Color(0xFFFFB800),
+          secondary: Color(0xFF453200),
+          surface: Color(0xFFFFFFFF),
+          background: Color(0xFFFFFFFF),
+          error: Color(0xFFC00000),
+          onPrimary: Color(0xFFFFFFFF),
+          onSecondary: Color(0xFFFFFFFF),
+          onSurface: Color(0xFF171000),
+          onBackground: Color(0xFF171000),
+          onError: Color(0xFFFFFFFF),
+          brightness: Brightness.light,
+        ),
+        textTheme: const TextTheme(
+          displayLarge: TextStyle(fontFamily: 'Inter', fontSize: 24, fontWeight: FontWeight.bold),
+          displayMedium: TextStyle(fontFamily: 'Inter', fontSize: 16, fontWeight: FontWeight.bold),
+          displaySmall: TextStyle(fontFamily: 'Inter', fontSize: 16, fontWeight: FontWeight.w600),
+          headlineMedium: TextStyle(fontFamily: 'Inter', fontSize: 8, fontWeight: FontWeight.bold),
+          bodyLarge: TextStyle(fontFamily: 'Inter', fontSize: 16, fontWeight: FontWeight.normal),
+          bodySmall: TextStyle(fontFamily: 'Inter', fontSize: 14, fontWeight: FontWeight.normal),
+        ),
+        useMaterial3: false,
       ),
       routerConfig: PageRouter.router(),
     );