feat：增加数据库迁移文件

database/migrations/2026_05_08_100000_create_currencies_table.php

@@ -0,0 +1,26 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('currencies', function (Blueprint $table) {
+            $table->id();
+            $table->string('code', 16)->unique();
+            $table->string('name', 64);
+            $table->unsignedTinyInteger('decimal_places')->default(2);
+            $table->boolean('is_enabled')->default(true);
+            $table->boolean('is_bettable')->default(false);
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('currencies');
+    }
+};