feat: 第四阶段财务与人事薪资模块

- 新增2个migration(11张表): finance(6表)/hr(5表)
- 新增11个Model + 11个Controller
- 新增50条API路由(总计262条)
- 新增2个前端API模块 + 10个管理页面
- 迁移运行通过, vite build验证通过

backend/app/Models/Finance/CustomerAccount.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Models\Finance;
+
+use App\Models\Crm\Customer;
+use App\Traits\BelongsToStore;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class CustomerAccount extends Model
+{
+    use BelongsToStore;
+
+    protected $fillable = [
+        'store_id', 'customer_id', 'cash_balance', 'card_balance', 'points',
+    ];
+
+    protected function casts(): array
+    {
+        return [
+            'cash_balance' => 'decimal:2',
+            'card_balance' => 'decimal:2',
+            'points' => 'integer',
+        ];
+    }
+
+    public function customer(): BelongsTo
+    {
+        return $this->belongsTo(Customer::class);
+    }
+
+    public function transactions(): HasMany
+    {
+        return $this->hasMany(AccountTransaction::class, 'customer_account_id');
+    }
+}