Add issue attachments

- IssueAttachment link table (issue <-> file) + migration
- GET/POST /issues/:issueId/attachments, DELETE .../attachments/:fileId
- Only own uploaded files can be attached; attach is idempotent
- Registers issues as a file owner: attached files stay visible to issue
  participants and are not collected by GC
- IssueDetail.attachments GraphQL field via @ResolveField, issue module untouched

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/modules/issue-attachment/application/services/issue-attachment-expander.service.ts

@@ -0,0 +1,24 @@
+import { Injectable } from '@nestjs/common';
+import { IssueAttachment } from '../../domain/entities/issue-attachment.entity.js';
+import { IssueAttachmentDto } from '../dto/issue-attachment.dto.js';
+import { GetFilesUseCase } from '../../../file/application/use-cases/get-files/get-files.use-case.js';
+import { GetFilesQuery } from '../../../file/application/use-cases/get-files/get-files.query.js';
+
+/** Раскрывает вложения в метаданные файлов из file-модуля */
+@Injectable()
+export class IssueAttachmentExpanderService {
+  constructor(private readonly getFilesUseCase: GetFilesUseCase) {}
+
+  async expandAll(attachments: IssueAttachment[]): Promise<IssueAttachmentDto[]> {
+    if (attachments.length === 0) return [];
+
+    const files = await this.getFilesUseCase.execute(new GetFilesQuery(attachments.map((a) => a.fileId)));
+    const filesById = new Map(files.map((file) => [file.id, file]));
+
+    // Файл могли удалить между запросами — такое вложение просто не показываем
+    return attachments.flatMap((attachment) => {
+      const file = filesById.get(attachment.fileId);
+      return file ? [{ issueId: attachment.issueId, file, attachedAt: attachment.createdAt }] : [];
+    });
+  }
+}