Add blog thumbnail and banner upload endpoints with storage keys.

Store image filenames in DB, resolve paths for cleanup on replace/delete, and reuse product-thumb multer limits.

backend/src/modules/blog/config/blogImageUpload.ts

@@ -0,0 +1,12 @@
+import { getProductThumbMulterConfig } from '../../../config';
+import { getBlogImagesDir } from '../../../config/uploadPaths';
+import { createDiskStorageUploadOptions } from '../../../utils/createDiskStorageUploadOptions';
+import { createUploadFilePipe } from '../../../utils/createUploadFilePipe';
+
+const uploadDir = getBlogImagesDir();
+
+export const blogImageUploadOptions = createDiskStorageUploadOptions(uploadDir);
+
+const { allowedMimes, maxFileBytes } = getProductThumbMulterConfig();
+
+export const blogImageFilePipe = createUploadFilePipe(allowedMimes, maxFileBytes);