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/ServiceExecution.php

@@ -0,0 +1,15 @@
+<?php
+namespace App\Models\Service;
+use App\Models\Crm\Customer;
+use App\Models\User;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+class ServiceExecution extends Model
+{
+    protected $fillable = ['service_order_id','service_item_id','customer_id','technician_id','scheduled_at','started_at','ended_at','status','remark'];
+    protected function casts(): array { return ['scheduled_at'=>'datetime','started_at'=>'datetime','ended_at'=>'datetime','status'=>'integer']; }
+    public function order(): BelongsTo { return $this->belongsTo(ServiceOrder::class, 'service_order_id'); }
+    public function serviceItem(): BelongsTo { return $this->belongsTo(ServiceItem::class); }
+    public function customer(): BelongsTo { return $this->belongsTo(Customer::class); }
+    public function technician(): BelongsTo { return $this->belongsTo(User::class, 'technician_id'); }
+}