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/lib/i18n/strings.g.dart

@@ -3,10 +3,10 @@
 /// Source: lib/i18n
 /// To regenerate, run: `dart run slang`
 ///
-/// Locales: 2
-/// Strings: 572 (286 per locale)
+/// Locales: 3
+/// Strings: 861 (287 per locale)
 ///
-/// Built on 2026-07-09 at 20:28 UTC
+/// Built on 2026-07-09 at 20:35 UTC
 
 // coverage:ignore-file
 // ignore_for_file: type=lint, unused_import
@@ -19,6 +19,7 @@ import 'package:slang_flutter/slang_flutter.dart';
 export 'package:slang_flutter/slang_flutter.dart';
 
 import 'strings_es.g.dart' as l_es;
+import 'strings_pt.g.dart' as l_pt;
 part 'strings_en.g.dart';
 
 /// Supported locales.
@@ -29,7 +30,8 @@ part 'strings_en.g.dart';
 /// - if (LocaleSettings.currentLocale == AppLocale.en) // locale check
 enum AppLocale with BaseAppLocale<AppLocale, Translations> {
 	en(languageCode: 'en'),
-	es(languageCode: 'es');
+	es(languageCode: 'es'),
+	pt(languageCode: 'pt');
 
 	const AppLocale({
 		required this.languageCode,
@@ -73,6 +75,12 @@ enum AppLocale with BaseAppLocale<AppLocale, Translations> {
 					cardinalResolver: cardinalResolver,
 					ordinalResolver: ordinalResolver,
 				);
+			case AppLocale.pt:
+				return l_pt.TranslationsPt(
+					overrides: overrides,
+					cardinalResolver: cardinalResolver,
+					ordinalResolver: ordinalResolver,
+				);
 		}
 	}