feat: [roadmap] 중장기 계획 테이블 마이그레이션 추가

- admin_roadmap_plans: 계획 테이블 (제목, 카테고리, 상태, Phase, 진행률 등)
- admin_roadmap_milestones: 마일스톤 테이블 (plan_id FK, 상태, 예정일 등)

database/migrations/2026_03_02_000000_create_admin_roadmap_tables.php

@@ -0,0 +1,68 @@
+<?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('admin_roadmap_plans', function (Blueprint $table) {
+            $table->id();
+            $table->string('title', 200);
+            $table->text('description')->nullable();
+            $table->longText('content')->nullable();
+            $table->string('category', 30)->default('general');
+            $table->string('status', 20)->default('planned');
+            $table->string('priority', 10)->default('medium');
+            $table->string('phase', 30)->default('phase_1');
+            $table->date('start_date')->nullable();
+            $table->date('end_date')->nullable();
+            $table->tinyInteger('progress')->unsigned()->default(0);
+            $table->string('color', 7)->default('#3B82F6');
+            $table->integer('sort_order')->default(0);
+            $table->unsignedBigInteger('created_by')->nullable();
+            $table->unsignedBigInteger('updated_by')->nullable();
+            $table->unsignedBigInteger('deleted_by')->nullable();
+            $table->timestamps();
+            $table->softDeletes();
+
+            $table->index('category');
+            $table->index('status');
+            $table->index('phase');
+            $table->index('priority');
+        });
+
+        Schema::create('admin_roadmap_milestones', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('plan_id');
+            $table->string('title', 255);
+            $table->text('description')->nullable();
+            $table->string('status', 20)->default('pending');
+            $table->date('due_date')->nullable();
+            $table->timestamp('completed_at')->nullable();
+            $table->unsignedBigInteger('assignee_id')->nullable();
+            $table->integer('sort_order')->default(0);
+            $table->unsignedBigInteger('created_by')->nullable();
+            $table->unsignedBigInteger('updated_by')->nullable();
+            $table->unsignedBigInteger('deleted_by')->nullable();
+            $table->timestamps();
+            $table->softDeletes();
+
+            $table->foreign('plan_id')
+                ->references('id')
+                ->on('admin_roadmap_plans')
+                ->cascadeOnDelete();
+
+            $table->index('status');
+            $table->index('due_date');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('admin_roadmap_milestones');
+        Schema::dropIfExists('admin_roadmap_plans');
+    }
+};