Image URLs in Markdown Exports and API Responses are Local Paths Instead of Public S3 URLs

Issue Description I have deployed Docmost using Docker and successfully integrated it with an S3-compatible cloud storage provider. Within the Docmost web interface, image uploads and rendering work perfectly, and I can confirm that the images are being successfully stored in the S3 bucket. However, I've encountered a critical issue with two key features: Markdown Export: When I export a document as a Markdown file, all image URLs are local server paths, formatted like files/some-image.png. API Content Fetching: When retrieving document content via the GET /api/docs/{id} endpoint, the returned JSON data also contains the same local image path, api/files/some-image.png. Expected Behavior For both Markdown exports and API responses, any image that has been uploaded to S3 should have its URL automatically resolved to its public S3 URL (e.g., not the internal API path of the Docmost instance. Impact This issue significantly undermines the content's portability and…