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/ai_digest/data/llm_digest_config.dart

@@ -0,0 +1,77 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/features/ai_digest/domain/ai_digest_models.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+const String _enabledKey = 'llm_digest_enabled';
+const String _preferredWeekdayKey = 'llm_digest_preferred_weekday';
+const String _preferredHourKey = 'llm_digest_preferred_hour';
+const String _requireWifiKey = 'llm_digest_require_wifi';
+const String _requireChargingKey = 'llm_digest_require_charging';
+
+class LlmDigestConfigNotifier extends Notifier<LlmDigestConfigState> {
+  Future<void>? _initializeFuture;
+
+  @override
+  LlmDigestConfigState build() {
+    return const LlmDigestConfigState();
+  }
+
+  Future<void> initialize() {
+    _initializeFuture ??= _initializeFromStorage();
+    return _initializeFuture!;
+  }
+
+  Future<void> _initializeFromStorage() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    state = LlmDigestConfigState(
+      enabled: prefs.getBool(_enabledKey) ?? false,
+      preferredWeekday: prefs.getInt(_preferredWeekdayKey) ?? DateTime.sunday,
+      preferredHour: prefs.getInt(_preferredHourKey) ?? 21,
+      requireWifi: prefs.getBool(_requireWifiKey) ?? true,
+      requireCharging: prefs.getBool(_requireChargingKey) ?? true,
+    );
+  }
+
+  Future<void> setEnabled(bool enabled) async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.setBool(_enabledKey, enabled);
+    state = state.copyWith(enabled: enabled);
+  }
+
+  Future<void> setPreferredRunWindow({
+    required int weekday,
+    required int hour,
+  }) async {
+    final int normalizedWeekday = weekday.clamp(
+      DateTime.monday,
+      DateTime.sunday,
+    );
+    final int normalizedHour = hour.clamp(0, 23);
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.setInt(_preferredWeekdayKey, normalizedWeekday);
+    await prefs.setInt(_preferredHourKey, normalizedHour);
+    state = state.copyWith(
+      preferredWeekday: normalizedWeekday,
+      preferredHour: normalizedHour,
+    );
+  }
+
+  Future<void> setNetworkPolicy({
+    required bool requireWifi,
+    required bool requireCharging,
+  }) async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.setBool(_requireWifiKey, requireWifi);
+    await prefs.setBool(_requireChargingKey, requireCharging);
+    state = state.copyWith(
+      requireWifi: requireWifi,
+      requireCharging: requireCharging,
+    );
+  }
+}
+
+final NotifierProvider<LlmDigestConfigNotifier, LlmDigestConfigState>
+llmDigestConfigProvider =
+    NotifierProvider<LlmDigestConfigNotifier, LlmDigestConfigState>(
+      LlmDigestConfigNotifier.new,
+    );