feat(API): 역할/권한 관리 API 개선

- RoleController: 역할 CRUD API 개선
- RolePermissionController: 역할별 권한 설정 API 추가
- RoleService/RolePermissionService: 비즈니스 로직 분리
- Role 모델: is_hidden 필드 추가 (시스템 역할 숨김)
- 역할 숨김 마이그레이션 추가

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

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

database/migrations/2025_12_30_160802_add_is_hidden_to_roles_table.php

@@ -0,0 +1,31 @@
+<?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('roles', function (Blueprint $table) {
+            $table->boolean('is_hidden')
+                ->default(false)
+                ->after('description')
+                ->comment('숨김 여부 (공개/숨김)');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('roles', function (Blueprint $table) {
+            $table->dropColumn('is_hidden');
+        });
+    }
+};