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/core/llm/llm_config.dart

@@ -0,0 +1,107 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+
+const String _llmApiKeyStorageKey = 'llm_api_key';
+const String _llmProviderStorageKey = 'llm_provider';
+
+enum LlmProvider { openai, anthropic, google }
+
+class LlmConfigState {
+  const LlmConfigState({
+    this.apiKeyConfigured = false,
+    this.provider = LlmProvider.openai,
+    this.isConfigured = false,
+  });
+
+  final bool apiKeyConfigured;
+  final LlmProvider provider;
+  final bool isConfigured;
+
+  LlmConfigState copyWith({
+    bool? apiKeyConfigured,
+    LlmProvider? provider,
+    bool? isConfigured,
+  }) {
+    return LlmConfigState(
+      apiKeyConfigured: apiKeyConfigured ?? this.apiKeyConfigured,
+      provider: provider ?? this.provider,
+      isConfigured: isConfigured ?? this.isConfigured,
+    );
+  }
+}
+
+class LlmConfigNotifier extends Notifier<LlmConfigState> {
+  Future<void>? _initializeFuture;
+
+  @override
+  LlmConfigState build() {
+    return const LlmConfigState();
+  }
+
+  Future<void> initialize() async {
+    final Future<void>? inFlight = _initializeFuture;
+    if (inFlight != null) {
+      return inFlight;
+    }
+    _initializeFuture = _initializeFromStorage();
+    return _initializeFuture;
+  }
+
+  Future<void> _initializeFromStorage() async {
+    const FlutterSecureStorage secureStorage = FlutterSecureStorage();
+    final String? storedKey = await secureStorage.read(
+      key: _llmApiKeyStorageKey,
+    );
+    final String? storedProvider = await secureStorage.read(
+      key: _llmProviderStorageKey,
+    );
+
+    state = LlmConfigState(
+      apiKeyConfigured: storedKey != null && storedKey.isNotEmpty,
+      provider: storedProvider != null
+          ? LlmProvider.values.firstWhere(
+              (LlmProvider p) => p.name == storedProvider,
+              orElse: () => LlmProvider.openai,
+            )
+          : LlmProvider.openai,
+      isConfigured: storedKey != null && storedKey.isNotEmpty,
+    );
+  }
+
+  Future<void> setApiKey(String apiKey) async {
+    const FlutterSecureStorage secureStorage = FlutterSecureStorage();
+    if (apiKey.isEmpty) {
+      await secureStorage.delete(key: _llmApiKeyStorageKey);
+    } else {
+      await secureStorage.write(key: _llmApiKeyStorageKey, value: apiKey);
+    }
+    state = state.copyWith(
+      apiKeyConfigured: apiKey.isNotEmpty,
+      isConfigured: apiKey.isNotEmpty,
+    );
+  }
+
+  Future<void> setProvider(LlmProvider provider) async {
+    const FlutterSecureStorage secureStorage = FlutterSecureStorage();
+    await secureStorage.write(
+      key: _llmProviderStorageKey,
+      value: provider.name,
+    );
+    state = state.copyWith(provider: provider);
+  }
+
+  Future<String?> getApiKey() async {
+    const FlutterSecureStorage secureStorage = FlutterSecureStorage();
+    return secureStorage.read(key: _llmApiKeyStorageKey);
+  }
+
+  Future<void> clearApiKey() async {
+    const FlutterSecureStorage secureStorage = FlutterSecureStorage();
+    await secureStorage.delete(key: _llmApiKeyStorageKey);
+    state = state.copyWith(apiKeyConfigured: false, isConfigured: false);
+  }
+}
+
+final llmConfigProvider = NotifierProvider<LlmConfigNotifier, LlmConfigState>(
+  LlmConfigNotifier.new,
+);