feat: dynamic units table with localized names via GET /units

- Add units + unit_translations tables with FK constraints on products and ingredient_mappings
- Normalize products.unit from Russian strings (г, кг) to English codes (g, kg)
- Load units at startup (in-memory registry) and serve via GET /units (language-aware)
- Replace hardcoded _units lists and _mapUnit() functions in Flutter with unitsProvider FutureProvider
- Re-fetches automatically when language changes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/features/recipes/recipe_detail_screen.dart

@@ -3,6 +3,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import '../../core/locale/unit_provider.dart';
 import '../../core/theme/app_colors.dart';
 import '../../shared/models/recipe.dart';
 import '../../shared/models/saved_recipe.dart';
@@ -370,13 +371,13 @@ class _TagsRow extends StatelessWidget {
   }
 }
 
-class _IngredientsSection extends StatelessWidget {
+class _IngredientsSection extends ConsumerWidget {
   final List<RecipeIngredient> ingredients;
 
   const _IngredientsSection({required this.ingredients});
 
   @override
-  Widget build(BuildContext context) {
+  Widget build(BuildContext context, WidgetRef ref) {
     if (ingredients.isEmpty) return const SizedBox.shrink();
 
     return Padding(
@@ -401,7 +402,7 @@ class _IngredientsSection extends StatelessWidget {
                   const SizedBox(width: 10),
                   Expanded(child: Text(ing.name)),
                   Text(
-                    '${_formatAmount(ing.amount)} ${ing.unit}',
+                    '${_formatAmount(ing.amount)} ${ref.watch(unitsProvider).valueOrNull?[ing.unit] ?? ing.unit}',
                     style: const TextStyle(
                         color: AppColors.textSecondary, fontSize: 13),
                   ),