feat:sales_consultations 테이블에 tenant_prospect_id 컬럼 추가

- 가망고객(prospect) 상담 기록 지원을 위해 tenant_prospect_id 컬럼 추가
- tenant_id를 nullable로 변경 (가망고객일 경우 null)
- tenant_prospect_id 인덱스 추가

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

database/migrations/2026_01_31_210000_add_tenant_prospect_id_to_sales_consultations.php

@@ -0,0 +1,43 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     * sales_consultations 테이블에 tenant_prospect_id 컬럼 추가 (가망고객 상담 기록 지원)
+     */
+    public function up(): void
+    {
+        Schema::table('sales_consultations', function (Blueprint $table) {
+            // tenant_prospect_id 컬럼 추가 (tenant_id 다음에)
+            $table->unsignedBigInteger('tenant_prospect_id')
+                ->nullable()
+                ->after('tenant_id')
+                ->comment('가망고객 ID (테넌트 전환 전)');
+
+            // tenant_id를 nullable로 변경 (가망고객일 경우 null)
+            $table->unsignedBigInteger('tenant_id')->nullable()->change();
+
+            // 인덱스 추가
+            $table->index(['tenant_prospect_id', 'scenario_type'], 'consultations_prospect_scenario_idx');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('sales_consultations', function (Blueprint $table) {
+            $table->dropIndex('consultations_prospect_scenario_idx');
+            $table->dropColumn('tenant_prospect_id');
+
+            // tenant_id를 다시 not nullable로 변경
+            $table->unsignedBigInteger('tenant_id')->nullable(false)->change();
+        });
+    }
+};