WebDAV: Share PNG and vector files when an upload size is configured

As a user who uploads photos to a WebDAV service at a reduced size, I want my PNG and vector files to be included, so that a sized upload is not silently missing files.

Background

When a service is configured to upload files at a specific size, rather than as unmodified originals, two gaps show up:

• A photo whose only image file is a PNG is not uploaded at all. Screenshots are the common case.
• A vector graphic such as .svg, .ai, or .eps is uploaded as the original, while the preview generated for it is left out.

The rules that pick the files to upload predate PNG becoming a preview format, and were never revisited.

Open Questions

• Should a vector graphic be uploaded as the original? Vectors are resolution independent, so the original may scale better than any preview rendered from it.
• How should a file be named when its format changes on the way out? Services may already hold copies under the names used today.

Acceptance Criteria

• A photo whose only image file is a PNG MUST be uploaded when a specific size is configured
• The name a file is uploaded under MUST match the format of its contents
• Formats that upload correctly today MUST keep their current names and behavior
• The intended behavior for vector graphics SHOULD be decided and documented