feat: [boards] 게시판 API 시스템 구현

- BoardController, PostController 추가
- Board, BoardSetting 모델 수정
- BoardService 추가
- FormRequest 클래스 추가
- Swagger 문서 추가 (BoardApi, PostApi)
- 게시판 시스템 필드 마이그레이션 추가

app/Http/Requests/Boards/BoardUpdateRequest.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace App\Http\Requests\Boards;
+
+use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
+
+class BoardUpdateRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        $boardId = $this->route('id');
+
+        return [
+            'board_code' => [
+                'sometimes',
+                'string',
+                'max:50',
+                Rule::unique('boards', 'board_code')->ignore($boardId),
+            ],
+            'board_type' => 'nullable|string|max:50',
+            'name' => 'sometimes|string|max:100',
+            'description' => 'nullable|string|max:500',
+            'editor_type' => 'sometimes|string|in:wysiwyg,markdown,text',
+            'allow_files' => 'sometimes|boolean',
+            'max_file_count' => 'sometimes|integer|min:0|max:20',
+            'max_file_size' => 'sometimes|integer|min:0|max:102400',
+            'extra_settings' => 'nullable|array',
+            'extra_settings.permissions' => 'nullable|array',
+            'extra_settings.permissions.read' => 'nullable|array',
+            'extra_settings.permissions.write' => 'nullable|array',
+            'extra_settings.permissions.manage' => 'nullable|array',
+            'is_active' => 'sometimes|boolean',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'board_code.unique' => __('validation.unique', ['attribute' => '게시판 코드']),
+        ];
+    }
+}