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/app/navigation/README.md

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+# App Navigation
+
+This folder contains typed shell destinations used by the main app shell.
+
+Change `app_destination.dart` when you add, remove, or rename a top-level tab.
+The shell in `../presentation/` maps these destinations to screens.

lib/app/navigation/app_destination.dart

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+import 'package:flutter/material.dart';
+
+/// Typed shell destinations used by the app navigation shell.
+enum AppDestination {
+  dashboard('Dashboard', Icons.dashboard_rounded),
+  people('People', Icons.people_alt_rounded),
+  moments('Moments', Icons.auto_awesome_rounded),
+  signals('Signals', Icons.tips_and_updates_rounded),
+  aiReview('AI Review', Icons.rate_review_rounded),
+  ideas('Ideas', Icons.lightbulb_outline_rounded),
+  reminders('Reminders', Icons.notifications_active_outlined),
+  sync('Sync', Icons.sync_rounded),
+  settings('Settings', Icons.settings_rounded);
+
+  const AppDestination(this.label, this.icon);
+
+  final String label;
+  final IconData icon;
+}
+
+/// Secondary destinations exposed from the compact shell overflow menu.
+enum CompactSecondaryDestination { aiReview, ideas, reminders, sync, settings }