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/mappers/file-application.mapper.ts

@@ -0,0 +1,16 @@
+import { StoredFile } from '../../domain/entities/stored-file.entity.js';
+import { FileDto } from '../dto/file.dto.js';
+
+export class FileApplicationMapper {
+  /** storageKey — деталь хранилища, наружу не отдаём */
+  static toDto(file: StoredFile): FileDto {
+    return {
+      id: file.id as string,
+      fileName: file.fileName,
+      mimeType: file.mimeType,
+      size: file.size,
+      uploaderId: file.uploaderId,
+      createdAt: file.createdAt,
+    };
+  }
+}