i18n: RTL smoke tests, Portuguese locale and a translation guide

- Add rtl_smoke_test covering inventory, detail (lot sheet) and settings
  under Directionality.rtl, with an Arabic label and vernacular name.
- Ship pt.i18n.json (Portuguese) as proof the locale pipeline scales beyond
  es/en; wire its language tile in Settings.
- docs/i18n.md documents the Weblate-ready flow for adding locales.

apps/app_seeds/test/ui/rtl_smoke_test.dart

@@ -0,0 +1,99 @@
+import 'package:commons_core/commons_core.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/database.dart';
+import 'package:tane/db/enums.dart';
+import 'package:tane/ui/inventory_list_screen.dart';
+import 'package:tane/ui/settings_screen.dart';
+
+import '../support/test_support.dart';
+
+/// RTL is a first-class requirement (CLAUDE.md): the main screens must build
+/// and lay out under right-to-left without overflowing or misplacing
+/// directional affordances. Overflow errors fail these tests automatically.
+void main() {
+  late AppDatabase db;
+
+  setUp(() => db = newTestDatabase());
+  tearDown(() => db.close());
+
+  testWidgets('the inventory list renders under RTL', (tester) async {
+    final repo = newTestRepository(db);
+    final id = await repo.addQuickVariety(
+      label: 'طماطم بلدية', // an Arabic label, as a keeper would write it
+      category: 'Solanaceae',
+    );
+    await repo.addLot(
+      varietyId: id,
+      harvestYear: 2024,
+      quantity: const Quantity(kind: QuantityKind.handful),
+      offerStatus: OfferStatus.shared,
+    );
+    await repo.addQuickVariety(label: 'Maize', category: 'Poaceae');
+
+    await tester.pumpWidget(
+      wrapScreen(
+        repository: repo,
+        textDirection: TextDirection.rtl,
+        child: const InventoryListScreen(),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.text('طماطم بلدية'), findsOneWidget);
+    expect(find.byKey(const Key('inventory.filter.sharing')), findsOneWidget);
+    await disposeTree(tester);
+  });
+
+  testWidgets('the variety detail (lots, calendar, names) renders under RTL', (
+    tester,
+  ) async {
+    final repo = newTestRepository(db);
+    final id = await repo.addQuickVariety(
+      label: 'Grandma tomato',
+      category: 'Solanaceae',
+    );
+    await repo.addVernacularName(id, 'طماطم');
+    await repo.addLot(
+      varietyId: id,
+      harvestYear: 2023,
+      quantity: const Quantity(kind: QuantityKind.packet, count: 3),
+      abundance: Abundance.plentyToShare,
+      offerStatus: OfferStatus.exchange,
+    );
+
+    await tester.pumpWidget(
+      wrapDetail(
+        repository: repo,
+        varietyId: id,
+        species: newTestSpeciesRepository(db),
+        textDirection: TextDirection.rtl,
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.text('Grandma tomato'), findsOneWidget);
+    expect(find.text('طماطم'), findsOneWidget);
+
+    // The lot sheet (the busiest form) must also lay out under RTL.
+    await tester.tap(find.byKey(const Key('detail.addLot')));
+    await tester.pumpAndSettle();
+    expect(find.byKey(const Key('addLot.save')), findsOneWidget);
+    await disposeTree(tester);
+  });
+
+  testWidgets('settings renders under RTL', (tester) async {
+    final repo = newTestRepository(db);
+    await tester.pumpWidget(
+      wrapScreen(
+        repository: repo,
+        textDirection: TextDirection.rtl,
+        child: const SettingsScreen(),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.text('Português'), findsOneWidget);
+    await disposeTree(tester);
+  });
+}