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/shared/README.md

@@ -0,0 +1,4 @@
+# Shared Feature UI
+
+Only genuinely reusable feature-facing widgets belong here. If a widget is owned
+by one slice, keep it inside that slice to avoid horizontal drift.

lib/features/shared/frosted_card.dart

@@ -1,40 +1,2 @@
-import 'dart:ui';
-
-import 'package:flutter/material.dart';
-
-class FrostedCard extends StatelessWidget {
-  const FrostedCard({
-    required this.child,
-    super.key,
-    this.padding = const EdgeInsets.all(20),
-  });
-
-  final Widget child;
-  final EdgeInsetsGeometry padding;
-
-  @override
-  Widget build(BuildContext context) {
-    return ClipRRect(
-      borderRadius: BorderRadius.circular(24),
-      child: BackdropFilter(
-        filter: ImageFilter.blur(sigmaX: 12, sigmaY: 12),
-        child: Container(
-          padding: padding,
-          decoration: BoxDecoration(
-            color: Colors.white.withValues(alpha: 0.72),
-            borderRadius: BorderRadius.circular(24),
-            border: Border.all(color: Colors.white.withValues(alpha: 0.6)),
-            boxShadow: const <BoxShadow>[
-              BoxShadow(
-                color: Color(0x14000000),
-                blurRadius: 24,
-                offset: Offset(0, 12),
-              ),
-            ],
-          ),
-          child: child,
-        ),
-      ),
-    );
-  }
-}
+// Legacy compatibility export for the shared frosted card widget.
+export 'package:relationship_saver/core/presentation/frosted_card.dart';