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/observability/sentry_init.dart

@@ -0,0 +1,63 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/config/app_config.dart';
+import 'package:sentry_flutter/sentry_flutter.dart';
+
+class SentryInit {
+  SentryInit();
+
+  Future<void>? _initializeFuture;
+  bool _initialized = false;
+
+  Future<void> initialize({FutureOr<void> Function()? appRunner}) async {
+    final Future<void>? inFlight = _initializeFuture;
+    if (inFlight != null) {
+      await inFlight;
+      if (appRunner != null && !_initialized) {
+        await Future<void>.sync(appRunner);
+      }
+      return;
+    }
+
+    _initializeFuture = _initializeInternal(appRunner: appRunner);
+    return _initializeFuture;
+  }
+
+  Future<void> _initializeInternal({
+    FutureOr<void> Function()? appRunner,
+  }) async {
+    if (!kReleaseMode || AppConfig.sentryDsn.isEmpty) {
+      if (appRunner != null) {
+        await Future<void>.sync(appRunner);
+      }
+      return;
+    }
+
+    await SentryFlutter.init((options) {
+      options.dsn = AppConfig.sentryDsn;
+      options.environment = AppConfig.useFakeBackend
+          ? 'development'
+          : 'production';
+      options.tracesSampleRate = 0.1;
+    }, appRunner: appRunner);
+    _initialized = true;
+  }
+
+  void captureException(Object error, {StackTrace? stackTrace}) {
+    if (_initialized) {
+      Sentry.captureException(error, stackTrace: stackTrace);
+    }
+  }
+
+  void captureMessage(String message, {SentryLevel level = SentryLevel.info}) {
+    if (_initialized) {
+      Sentry.captureMessage(message, level: level);
+    }
+  }
+}
+
+final sentryInitProvider = Provider<SentryInit>((Ref ref) {
+  return SentryInit();
+});