feat: initial Pyramid project scaffold

lib/core/app.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_localizations/flutter_localizations.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:pyramid/core/router.dart';
+import 'package:pyramid/core/theme.dart';
+
+class PyramidApp extends ConsumerWidget {
+  const PyramidApp({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final router = ref.watch(routerProvider);
+    final colorScheme = ref.watch(colorSchemeProvider);
+
+    return MaterialApp.router(
+      title: 'Pyramid',
+      theme: buildTheme(colorScheme, Brightness.light),
+      darkTheme: buildTheme(colorScheme, Brightness.dark),
+      themeMode: ThemeMode.system,
+      routerConfig: router,
+      localizationsDelegates: const [
+        GlobalMaterialLocalizations.delegate,
+        GlobalWidgetsLocalizations.delegate,
+        GlobalCupertinoLocalizations.delegate,
+      ],
+      supportedLocales: const [Locale('de'), Locale('en')],
+    );
+  }
+}

lib/core/router.dart

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+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:go_router/go_router.dart';
+import 'package:pyramid/layout/shell_page.dart';
+import 'package:pyramid/features/rooms/rooms_page.dart';
+import 'package:pyramid/features/chat/chat_page.dart';
+import 'package:pyramid/features/settings/settings_page.dart';
+
+final routerProvider = Provider<GoRouter>((ref) {
+  return GoRouter(
+    initialLocation: '/rooms',
+    routes: [
+      ShellRoute(
+        builder: (context, state, child) => ShellPage(child: child),
+        routes: [
+          GoRoute(
+            path: '/rooms',
+            builder: (context, state) => const RoomsPage(),
+          ),
+          GoRoute(
+            path: '/chat/:roomId',
+            builder: (context, state) =>
+                ChatPage(roomId: state.pathParameters['roomId']!),
+          ),
+          GoRoute(
+            path: '/settings',
+            builder: (context, state) => const SettingsPage(),
+          ),
+        ],
+      ),
+    ],
+  );
+});

lib/core/theme.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+final colorSchemeProvider = Provider<ColorScheme>((ref) {
+  return ColorScheme.fromSeed(
+    seedColor: const Color(0xFF6B4FA0),
+    brightness: Brightness.light,
+  );
+});
+
+ThemeData buildTheme(ColorScheme colorScheme, Brightness brightness) {
+  final scheme = brightness == Brightness.dark
+      ? ColorScheme.fromSeed(
+          seedColor: const Color(0xFF6B4FA0),
+          brightness: Brightness.dark,
+        )
+      : colorScheme;
+
+  return ThemeData(
+    colorScheme: scheme,
+    useMaterial3: true,
+    dividerTheme: const DividerThemeData(space: 1, thickness: 1),
+  );
+}