feat: 사용자 must_change_password 컬럼 추가

- users 테이블에 must_change_password 컬럼 추가 (boolean, default: false)
- 신규 사용자 생성/비밀번호 초기화 시 강제 비밀번호 변경 기능 지원

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

database/migrations/2025_12_01_232808_add_must_change_password_to_users_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->boolean('must_change_password')->default(false)->after('password');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->dropColumn('must_change_password');
+        });
+    }
+};