feat(j0.3): socle transverse (Result/Failure, theme, router, DI)

- core/error : Result<S> maison (Ok/Err) + Failure scellee avec egalite de valeur
- core/theme : AppTheme Material 3 (palette coucher, cibles tactiles enfant)
- core/router : routes nommees child/parentGate/parent (Navigator 1, placeholders)
- core/di : conventions providers
- CLAUDE.md §7 : Result maison & Navigator 1 actes (YAGNI)
- ROADMAP : 0.3 cochee, Jalon 0 termine
- corrections code review : egalite Failure, assertions tests, Map.unmodifiable

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/main.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:storytime/core/router/app_router.dart';
+import 'package:storytime/core/theme/app_theme.dart';
 
 void main() {
   runApp(const ProviderScope(child: StorytimeApp()));
@@ -9,17 +11,10 @@ class StorytimeApp extends StatelessWidget {
   const StorytimeApp({super.key});
 
   @override
-  Widget build(BuildContext context) {
-    return MaterialApp(
-      title: 'Storytime',
-      home: Scaffold(
-        body: Center(
-          child: Text(
-            'Storytime',
-            style: Theme.of(context).textTheme.headlineLarge,
-          ),
-        ),
-      ),
-    );
-  }
+  Widget build(BuildContext context) => MaterialApp(
+    title: 'Storytime',
+    theme: AppTheme.light(),
+    initialRoute: AppRoutes.child,
+    routes: appRoutes,
+  );
 }