Add file module for uploads and storage

- File model + migration: file metadata, content lives in object storage
- IFileStorage port with local disk and S3-compatible (RustFS/MinIO) adapters
- POST /files, GET /files/:id/download, DELETE /files/:id
- MIME sniffed from content; only safe images served inline, nosniff header
- FileOwnerRegistry: owner modules register to grant visibility and keep
  their files from GC; FileGcService removes orphaned files hourly
- TransformResponseInterceptor passes StreamableFile through

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

src/modules/file/application/use-cases/download-file/download-file.use-case.ts

@@ -0,0 +1,34 @@
+import type { Readable } from 'node:stream';
+import { Inject, Injectable } from '@nestjs/common';
+import { FILE_STORAGE, type IFileStorage } from '../../../domain/ports/file-storage.port.js';
+import { DownloadFileQuery } from './download-file.query.js';
+import { FileDto } from '../../dto/file.dto.js';
+import { FileApplicationMapper } from '../../mappers/file-application.mapper.js';
+import { FileAccessService } from '../../services/file-access.service.js';
+
+export interface DownloadFileResult {
+  file: FileDto;
+  /** Можно ли показывать в браузере inline, иначе — только скачивание */
+  inline: boolean;
+  stream: Readable;
+}
+
+@Injectable()
+export class DownloadFileUseCase {
+  constructor(
+    @Inject(FILE_STORAGE)
+    private readonly fileStorage: IFileStorage,
+    private readonly fileAccess: FileAccessService,
+  ) {}
+
+  async execute(query: DownloadFileQuery): Promise<DownloadFileResult> {
+    const file = await this.fileAccess.getVisibleFile(query.id, query.userId);
+    const stream = await this.fileStorage.get(file.storageKey);
+
+    return {
+      file: FileApplicationMapper.toDto(file),
+      inline: file.isInlineViewable,
+      stream,
+    };
+  }
+}