feat(search): 库存搜索支持拼音/首字母，按回车触发

- 新增 util.ToPinyin()，使用 go-pinyin 生成全拼和首字母
- Product model 新增 name_pinyin / name_initials 列（AutoMigrate）
- 启动时自动回填存量商品拼音
- Create / Update / FindOrCreate 写入时同步生成拼音
- 库存搜索 SQL 加入拼音/首字母 LIKE 条件
- 前端去掉 300ms 防抖，改为回车/点击搜索按钮触发

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

client/lib/screens/inventory/inventory_list_screen.dart

@@ -1,4 +1,3 @@
-import 'dart:async';
 import 'package:dio/dio.dart';
 import 'package:file_picker/file_picker.dart';
 import 'package:flutter/material.dart';
@@ -28,21 +27,16 @@ class InventoryListScreen extends ConsumerStatefulWidget {
 
 class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
   final _searchCtrl = TextEditingController();
-  Timer? _debounce;
   Set<String> _filterWarehouse = {};
 
   @override
   void dispose() {
     _searchCtrl.dispose();
-    _debounce?.cancel();
     super.dispose();
   }
 
-  void _onSearchChanged(String value) {
-    _debounce?.cancel();
-    _debounce = Timer(const Duration(milliseconds: 300), () {
-      ref.read(inventoryListProvider.notifier).setKeyword(value);
-    });
+  void _triggerSearch() {
+    ref.read(inventoryListProvider.notifier).setKeyword(_searchCtrl.text.trim());
   }
 
   Future<void> _editRemark(BuildContext context, Inventory item) async {
@@ -333,15 +327,20 @@ class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
                     ),
                     const Spacer(),
                     SizedBox(
-                      width: 200,
+                      width: 220,
                       child: TextField(
                         controller: _searchCtrl,
-                        decoration: const InputDecoration(
-                          hintText: '搜索商品名/编码',
-                          prefixIcon: Icon(Icons.search, size: 16),
-                          hintStyle: TextStyle(fontSize: 13),
+                        decoration: InputDecoration(
+                          hintText: '名称/编码/拼音，回车搜索',
+                          prefixIcon: const Icon(Icons.search, size: 16),
+                          hintStyle: const TextStyle(fontSize: 12),
+                          suffixIcon: IconButton(
+                            icon: const Icon(Icons.search, size: 16),
+                            tooltip: '搜索',
+                            onPressed: _triggerSearch,
+                          ),
                         ),
-                        onChanged: _onSearchChanged,
+                        onSubmitted: (_) => _triggerSearch(),
                       ),
                     ),
                   ],