add versioned image urls

[jamesmoore]

This pull request introduces improvements to image caching and cache busting in the application. It enables aggressive HTTP caching for image endpoints and adds a version query parameter to image URLs based on the file's last modification time, ensuring that clients always receive the latest image when it changes.

Caching improvements:

• Added the EnableCaching method to set HTTP response headers (Cache-Control: public, max-age=31536000, immutable) for both thumbnail and full image endpoints, allowing browsers to cache images for up to one year. [1] [2] [3]

Cache busting for image URLs:

• Updated the ImageFileViewModel to include a version parameter (derived from the image file's last modification timestamp) in image URLs. This ensures that when an image changes, the URL changes as well, invalidating the browser cache.
• Modified the ImageFileViewModelBuilder to pass the file's last write time as the version parameter when constructing the view model.

[Copilot]

Pull request overview

This PR improves client-side image caching by introducing cache-busting, versioned image URLs and by enabling long-lived HTTP caching headers on the image-serving endpoints.

Changes:

• Added a v= query parameter to thumbnail and full image URLs based on the image file’s last modification time.
• Updated the view model builder to compute and pass the file modification “version” into the view model.
• Added an EnableCaching helper and applied Cache-Control: public, max-age=31536000, immutable on image endpoints.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
SDMetaUI/Models/ImageFileViewModelBuilder.cs	Computes a version value from the file’s last write time and passes it into the view model.
SDMetaUI/Models/ImageFileViewModel.cs	Appends a v= query param to thumbnail/full image URLs for cache busting.
SDMetaUI/Controllers/ImagesController.cs	Enables aggressive caching headers for thumb/full image endpoints via a shared helper.

Suppressed comments (1)

SDMetaUI/Controllers/ImagesController.cs:52

• EnableCaching(httpResponse) is set before verifying the file exists, which means the NotFound/Problem paths can return a 1-year immutable Cache-Control header. Consider only enabling caching for successful file responses.

                EnableCaching(httpResponse);

                string physicalPath = Base32Decode(path);
                if (fileSystem.File.Exists(physicalPath))
                {

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