Implement S3 file deletion in MediaService

Description

The deleteFromS3() method in MediaService currently only logs a warning instead of performing actual S3 cleanup when media files are deleted.

Current Implementation

Located in apps/backend/src/media/media.service.ts:419, the method is a stub that needs to be implemented.

Required Implementation

The TODO outlines the following steps:

1. Parse the S3 key from the URL
2. Use AWS S3 client to delete the object(s)
3. Handle both main image and thumbnail files

Technical Details

• Method signature: private async deleteFromS3(imageUrl: string, thumbnailUrl?: string)
• Should handle both main image and optional thumbnail deletion
• Need to extract S3 keys from URLs and use AWS SDK for deletion
• Should include proper error handling

Impact

Without this implementation, deleted media files remain in S3 storage, leading to storage bloat and unnecessary costs.

Start in apps/backend/src/media/media.service.ts at MediaService.deleteFromS3() around line 419, then read the TODO and nearby AWS S3 usage. Implement the behavior for the main image and optional thumbnail, including URL-to-key handling and error handling. Done means deleted media no longer leaves those S3 objects behind.