Add video_thumbnail_keyframes support

[11bit]

Adds the video_thumbnail_keyframes / vtk option (imgproxy Pro), which was documented but had no implementation in this package.

video_thumbnail_keyframes:%keyframes
vtk:%keyframes

When set to 1, t or true, imgproxy uses the latest keyframe before the requested second for video thumbnail generation. This makes thumbnail generation faster, but the frame timestamp will not be exactly the requested one. Redefines the IMGPROXY_VIDEO_THUMBNAIL_KEYFRAMES config. Default: false.

The option is documented for processing URLs and under ## Info options in the image-info docs — the same position as video_thumbnail_second, which this package already treats as shared. It therefore lives in optionsShared/typesShared and is wired into both generateUrl and generateImageInfoUrl.

Implementation notes

• Follows the enforceThumbnail boolean pattern: test uses "key" in options, so an explicit false still emits vtk:f rather than being dropped.
• Marked **PRO feature** in the typedocs on both the value type and the *OptionsPartial interface, matching videoThumbnailSecond and the rest of the Pro options.

Verification

• tsc --noEmit clean, eslint src tests clean
• vitest run → 98 files / 1106 tests passing (11 new)
• End-to-end spot check: generateUrl(..., { width: 10, video_thumbnail_keyframes: true, video_thumbnail_second: 5 }) → /vtk:t/vts:5/w:10/plain/img; generateImageInfoUrl(..., { vtk: false }) → /vtk:f/plain/img

Relation to #85

Independent — branched from main, no overlap. Unlike bypass_cache/cache_tags in #85, vtk is already in the released 4.0.x docs, so it works against current imgproxy versions.

🤖 Generated with Claude Code

https://claude.ai/code/session_01G8Aa3xeVUCaxKtQJDzZhMo