feat: 第三阶段业务模块(服务产康/月嫂/进销存)

- 新增3个migration(15张表): service/nanny/inventory
- 新增15个Model + 13个Controller
- 新增55条API路由(总计212条)
- 新增3个前端API模块 + 11个管理页面
- vite build验证通过

backend/app/Models/Service/ServiceItem.php

@@ -0,0 +1,10 @@
+<?php
+namespace App\Models\Service;
+use App\Traits\BelongsToStore;
+use Illuminate\Database\Eloquent\Model;
+class ServiceItem extends Model
+{
+    use BelongsToStore;
+    protected $fillable = ['store_id','name','category','price','duration','description','image','status'];
+    protected function casts(): array { return ['category'=>'integer','price'=>'decimal:2','duration'=>'integer','status'=>'integer']; }
+}