feat(j0.1): squelette projet Flutter + arborescence clean archi

- flutter create --platforms=android --org biz.siteop
- arborescence lib/core/{error,theme,router,di} et lib/features/{locking,playback,podcasts,parental,limits}/{domain,application,data,presentation}
- pubspec.yaml : flutter_riverpod ^2.6.1 (YAGNI — autres paquets aux jalons suivants)
- lib/main.dart : ProviderScope + StorytimeApp (MaterialApp + écran placeholder)
- test/app_boots_test.dart : TDD Red→Green vérifié (flutter test vert, flutter analyze 0 issue)
- README.md : prérequis Flutter 3.41.6 / Dart 3.11.4

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

android/build.gradle.kts

@@ -0,0 +1,24 @@
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+val newBuildDir: Directory =
+    rootProject.layout.buildDirectory
+        .dir("../../build")
+        .get()
+rootProject.layout.buildDirectory.value(newBuildDir)
+
+subprojects {
+    val newSubprojectBuildDir: Directory = newBuildDir.dir(project.name)
+    project.layout.buildDirectory.value(newSubprojectBuildDir)
+}
+subprojects {
+    project.evaluationDependsOn(":app")
+}
+
+tasks.register<Delete>("clean") {
+    delete(rootProject.layout.buildDirectory)
+}