feat: 前端分離+功能api化

1. 新增資產管理CRUD、googleOAuth登入
2. 更改原記帳controller

app/Models/InvestmentTransaction.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class InvestmentTransaction extends Model
+{
+    protected $fillable = [
+        'holding_id',
+        'action',
+        'shares',
+        'price',
+        'fee',
+        'tax',
+        'traded_at',
+        'note',
+        'amount', // 實際投入金額（基金用）
+        'nav',    // 淨值（基金用）
+    ];
+
+    protected $casts = [
+        'traded_at' => 'date',
+    ];
+
+    public function holding()
+    {
+        return $this->belongsTo(InvestmentHolding::class, 'holding_id');
+    }
+}