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.

test/features/local/storage/local_repository_hive_migration_test.dart

@@ -52,7 +52,7 @@ void main() {
 
       final LocalDataRecord? migrated = await hiveStore.read();
       expect(migrated, isNotNull);
-      expect(migrated!.schemaVersion, 3);
+      expect(migrated!.schemaVersion, 5);
 
       final LocalDataRecord? legacyAfter = await legacyStore.read();
       expect(legacyAfter, isNull);