feat: add local-first private AI digest workflow

Migrate app code into canonical feature slices, add phone-only AI digest scheduling and review, wire local notification/background task support, and cover the flow with tests.

lib/features/auth/application/README.md

@@ -0,0 +1,4 @@
+# Auth Application
+
+This layer coordinates auth state and session lifecycle. Start here when you
+need to change how the app decides whether a user is signed in.

lib/features/auth/application/session_controller.dart

@@ -0,0 +1,76 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/auth/token_store.dart';
+import 'package:relationship_saver/integrations/backend/backend_gateway.dart';
+import 'package:relationship_saver/integrations/backend/backend_gateway_provider.dart';
+import 'package:relationship_saver/integrations/backend/models/backend_models.dart';
+
+/// Manages authenticated session lifecycle for app-level navigation.
+class SessionController extends AsyncNotifier<AuthSession?> {
+  @override
+  Future<AuthSession?> build() async {
+    return ref.read(tokenStoreProvider).read();
+  }
+
+  Future<void> signIn({
+    required SignInMethod method,
+    String? email,
+    String? password,
+    String? idToken,
+  }) async {
+    state = const AsyncLoading<AuthSession?>();
+
+    try {
+      final BackendGateway gateway = ref.read(backendGatewayProvider);
+      final AuthSession session = await gateway.signIn(
+        SignInRequest(
+          method: method,
+          email: email,
+          password: password,
+          idToken: idToken,
+        ),
+      );
+
+      // Ensure fake gateway sessions are also persisted.
+      await ref.read(tokenStoreProvider).write(session);
+      state = AsyncData<AuthSession?>(session);
+    } catch (error, stackTrace) {
+      state = AsyncError<AuthSession?>(error, stackTrace);
+    }
+  }
+
+  Future<void> signOut() async {
+    final BackendGateway gateway = ref.read(backendGatewayProvider);
+    final TokenStore tokenStore = ref.read(tokenStoreProvider);
+
+    try {
+      await gateway.signOut();
+    } catch (_) {
+      // Offline-first sign-out should always clear local session.
+    }
+
+    await tokenStore.clear();
+    state = const AsyncData<AuthSession?>(null);
+  }
+
+  Future<void> refreshProfile() async {
+    final AuthSession? current = state.asData?.value;
+    if (current == null) {
+      return;
+    }
+
+    try {
+      final UserProfile profile = await ref.read(backendGatewayProvider).me();
+      final AuthSession updated = current.copyWith(user: profile);
+      await ref.read(tokenStoreProvider).write(updated);
+      state = AsyncData<AuthSession?>(updated);
+    } catch (_) {
+      // Keep current state if profile refresh fails.
+    }
+  }
+}
+
+final AsyncNotifierProvider<SessionController, AuthSession?>
+sessionControllerProvider =
+    AsyncNotifierProvider<SessionController, AuthSession?>(
+      SessionController.new,
+    );