Improve shelf image previews and timestamp layout

[brzvsk]

What changed

• When a file card points to an image, Space preview detects it through its Uniform Type Identifier and renders the original file as an image
• The preview uses ImageIO downsampling sized for the larger Retina pane instead of the shelf card Quick Look thumbnail
• The Image search filter now includes image files as well as native clipboard image items, while ordinary files stay excluded
• Image-file filtering uses macOS content-type detection, so formats such as HEIC, WebP, SVG, and RAW do not need a hard-coded extension list
• Combining Image and File filters still returns each matching item once
• Non-image files keep the existing generic file preview and Quick Look action
• Relative timestamps stay on one line instead of wrapping inside narrow cards

Testing

• Debug app target builds successfully with Xcode 26.6
• All 187 CopyCore tests pass, including native images, image files, mixed multi-file items, non-image files, text-plus-Image search, and Image-plus-File composition
• Installed and launched a locally signed Debug build using the existing bundle identifier
• git diff --check passes

[tarikbc]

Thanks, this one is the strongest of the four. The tests are exactly what I would have asked for, and registering the SQL function through prepareDatabase is the right call for a DatabasePool.

I pushed one commit to the branch rather than sending you back and forth:

• imageFileURL asked the file system for each content type from inside PreviewPane.body, so it re-probed on every re-render and a network share could block the shelf. It now runs in a detached task keyed on the card, with the spinner FileImagePreview already has covering the wait so the generic icon never flashes first.

Two things I checked and deliberately left alone:

• NSImage(cgImage:size: .zero) is correct. I was suspicious, so I tested it: the size resolves from the CGImage, so the aspect ratio is right.
• I considered memoizing the UTType(filenameExtension:) lookup in ImageFileDetection, then measured it at 2.2 us per call. Ten thousand file rows would cost about 22 ms, and the lock a pool of concurrent readers would need costs more than that. I added a comment saying so, so nobody re-opens it.

Builds clean, 187 tests pass. Merging.