chore: [API] 문서/설정 업데이트

- LOGICAL_RELATIONSHIPS.md 관계 정보 추가
- Swagger 서버 설명 변경
- files 테이블 mime_type 컬럼 확장 마이그레이션

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

database/migrations/2026_03_11_213232_alter_files_table_extend_mime_type.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('files', function (Blueprint $table) {
+            $table->string('mime_type', 150)->change();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('files', function (Blueprint $table) {
+            $table->string('mime_type', 50)->change();
+        });
+    }
+};