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/products/add_product_screen.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import '../../core/locale/unit_provider.dart';
 import '../../shared/models/ingredient_mapping.dart';
 import 'product_provider.dart';
 
@@ -18,7 +19,7 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
   final _qtyController = TextEditingController(text: '1');
   final _daysController = TextEditingController(text: '7');
 
-  String _unit = 'шт';
+  String _unit = 'pcs';
   String? _category;
   String? _mappingId;
   bool _saving = false;
@@ -28,8 +29,6 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
   bool _searching = false;
   Timer? _debounce;
 
-  static const _units = ['г', 'кг', 'мл', 'л', 'шт'];
-
   @override
   void dispose() {
     _nameController.dispose();
@@ -69,8 +68,7 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
       _mappingId = mapping.id;
       _category = mapping.category;
       if (mapping.defaultUnit != null) {
-        // Map backend unit codes to display units
-        _unit = _mapUnit(mapping.defaultUnit!);
+        _unit = mapping.defaultUnit!;
       }
       if (mapping.storageDays != null) {
         _daysController.text = mapping.storageDays.toString();
@@ -79,21 +77,6 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
     });
   }
 
-  String _mapUnit(String backendUnit) {
-    switch (backendUnit.toLowerCase()) {
-      case 'g':
-        return 'г';
-      case 'kg':
-        return 'кг';
-      case 'ml':
-        return 'мл';
-      case 'l':
-        return 'л';
-      default:
-        return 'шт';
-    }
-  }
-
   Future<void> _submit() async {
     final name = _nameController.text.trim();
     if (name.isEmpty) {
@@ -170,7 +153,8 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
                                 ? Text(_categoryLabel(m.category!))
                                 : null,
                             trailing: m.defaultUnit != null
-                                ? Text(m.defaultUnit!,
+                                ? Text(
+                                    ref.watch(unitsProvider).valueOrNull?[m.defaultUnit!] ?? m.defaultUnit!,
                                     style:
                                         Theme.of(context).textTheme.bodySmall)
                                 : null,
@@ -197,15 +181,18 @@ class _AddProductScreenState extends ConsumerState<AddProductScreen> {
                   ),
                 ),
                 const SizedBox(width: 12),
-                DropdownButtonHideUnderline(
-                  child: DropdownButton<String>(
-                    value: _units.contains(_unit) ? _unit : _units.last,
-                    items: _units
-                        .map((u) =>
-                            DropdownMenuItem(value: u, child: Text(u)))
-                        .toList(),
-                    onChanged: (v) => setState(() => _unit = v!),
+                ref.watch(unitsProvider).when(
+                  data: (units) => DropdownButtonHideUnderline(
+                    child: DropdownButton<String>(
+                      value: units.containsKey(_unit) ? _unit : units.keys.first,
+                      items: units.entries
+                          .map((e) => DropdownMenuItem(value: e.key, child: Text(e.value)))
+                          .toList(),
+                      onChanged: (v) => setState(() => _unit = v!),
+                    ),
                   ),
+                  loading: () => const SizedBox(width: 60, child: LinearProgressIndicator()),
+                  error: (_, __) => const Text('?'),
                 ),
               ],
             ),

client/lib/features/products/products_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
+import '../../core/locale/unit_provider.dart';
 import '../../shared/models/product.dart';
 import 'product_provider.dart';
 
@@ -205,7 +206,7 @@ class _ProductTile extends ConsumerWidget {
         ),
         title: Text(product.name),
         subtitle: Text(
-          '${_formatQty(product.quantity)} ${product.unit}',
+          '${_formatQty(product.quantity)} ${ref.watch(unitsProvider).valueOrNull?[product.unit] ?? product.unit}',
           style: theme.textTheme.bodySmall,
         ),
         trailing: Column(
@@ -303,8 +304,6 @@ class _EditProductSheetState extends ConsumerState<_EditProductSheet> {
       TextEditingController(text: widget.product.storageDays.toString());
   bool _saving = false;
 
-  static const _units = ['г', 'кг', 'мл', 'л', 'шт'];
-
   @override
   void dispose() {
     _qtyController.dispose();
@@ -340,12 +339,16 @@ class _EditProductSheetState extends ConsumerState<_EditProductSheet> {
                 ),
               ),
               const SizedBox(width: 12),
-              DropdownButton<String>(
-                value: _units.contains(_unit) ? _unit : _units.first,
-                items: _units
-                    .map((u) => DropdownMenuItem(value: u, child: Text(u)))
-                    .toList(),
-                onChanged: (v) => setState(() => _unit = v!),
+              ref.watch(unitsProvider).when(
+                data: (units) => DropdownButton<String>(
+                  value: units.containsKey(_unit) ? _unit : units.keys.first,
+                  items: units.entries
+                      .map((e) => DropdownMenuItem(value: e.key, child: Text(e.value)))
+                      .toList(),
+                  onChanged: (v) => setState(() => _unit = v!),
+                ),
+                loading: () => const SizedBox(width: 60, child: LinearProgressIndicator()),
+                error: (_, __) => const Text('?'),
               ),
             ],
           ),