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/support/test_support.dart

@@ -60,6 +60,7 @@ Widget wrapScreen({
   required VarietyRepository repository,
   required Widget child,
   AppLocale locale = AppLocale.en,
+  TextDirection? textDirection,
 }) {
   LocaleSettings.setLocaleSync(locale);
   return TranslationProvider(
@@ -75,7 +76,9 @@ Widget wrapScreen({
             GlobalWidgetsLocalizations.delegate,
             GlobalCupertinoLocalizations.delegate,
           ],
-          home: child,
+          home: textDirection == null
+              ? child
+              : Directionality(textDirection: textDirection, child: child),
         ),
       ),
     ),
@@ -88,6 +91,7 @@ Widget wrapDetail({
   required String varietyId,
   SpeciesRepository? species,
   AppLocale locale = AppLocale.en,
+  TextDirection? textDirection,
 }) {
   LocaleSettings.setLocaleSync(locale);
   return TranslationProvider(
@@ -106,7 +110,12 @@ Widget wrapDetail({
             GlobalWidgetsLocalizations.delegate,
             GlobalCupertinoLocalizations.delegate,
           ],
-          home: const VarietyDetailScreen(),
+          home: textDirection == null
+              ? const VarietyDetailScreen()
+              : Directionality(
+                  textDirection: textDirection,
+                  child: const VarietyDetailScreen(),
+                ),
         ),
       ),
     ),