feat(inventory): month/year harvest date picker (schema v3)

Replace the free-text harvest year with a themed month/year picker:
a tappable field opens a green-styled dialog with month and year grids
(navigable, paginated years), month optional. Lots now read e.g.
"September 2021" or just "Year 2021".

- schema v3: add nullable Lot.harvest_month (1..12) + migration + tests
- repo/cubit propagate harvestMonth; localized month names (en/es) via slang

apps/app_seeds/test/db/migration_test.dart

@@ -11,19 +11,30 @@ void main() {
     verifier = SchemaVerifier(GeneratedHelper());
   });
 
-  test('freshly created database matches the exported schema v2', () async {
-    final schema = await verifier.schemaAt(2);
+  test('freshly created database matches the exported schema v3', () async {
+    final schema = await verifier.schemaAt(3);
     final db = AppDatabase(schema.newConnection());
-    await verifier.migrateAndValidate(db, 2);
+    await verifier.migrateAndValidate(db, 3);
     await db.close();
   });
 
   test(
-    'upgrades v1 → v2 (adds Lot.type) and matches the fresh schema',
+    'upgrades v1 → v3 (adds Lot.type, then harvestMonth) and matches the '
+    'fresh schema',
     () async {
       final connection = await verifier.startAt(1);
       final db = AppDatabase(connection);
-      await verifier.migrateAndValidate(db, 2);
+      await verifier.migrateAndValidate(db, 3);
+      await db.close();
+    },
+  );
+
+  test(
+    'upgrades v2 → v3 (adds Lot.harvestMonth) and matches the fresh schema',
+    () async {
+      final connection = await verifier.startAt(2);
+      final db = AppDatabase(connection);
+      await verifier.migrateAndValidate(db, 3);
       await db.close();
     },
   );

apps/app_seeds/test/db/schema/schema.dart

@@ -6,6 +6,7 @@ import 'package:drift/drift.dart';
 import 'package:drift/internal/migrations.dart';
 import 'schema_v1.dart' as v1;
 import 'schema_v2.dart' as v2;
+import 'schema_v3.dart' as v3;
 
 class GeneratedHelper implements SchemaInstantiationHelper {
   @override
@@ -15,10 +16,12 @@ class GeneratedHelper implements SchemaInstantiationHelper {
         return v1.DatabaseAtV1(db);
       case 2:
         return v2.DatabaseAtV2(db);
+      case 3:
+        return v3.DatabaseAtV3(db);
       default:
         throw MissingSchemaException(version, versions);
     }
   }
 
-  static const versions = const [1, 2];
+  static const versions = const [1, 2, 3];
 }