fix(ui): image preview no longer blocks clicks after closing

[kitlangton]

Problem

After closing the image preview, clicks on the timeline did nothing for a while (about 1 s at the shipped spring, about 4 s with slow motion on).

The preview keeps its Kobalte content mounted through the closing flight, using a CSS animation that runs for --image-preview-exit. #56997 raised that hold from 1800 to 3200 ms per second of spring. While the content stays mounted:

• Kobalte leaves body at pointer-events: none. It restores pointer events only when a modal layer's content unmounts.
• The transparent panel keeps Kobalte's inline pointer-events: auto, so it catches clicks over the middle of the page.

On beta, 300 ms after Esc, document.elementFromPoint over the page text returned DIV[data-slot=image-preview-body], with body.style.pointerEvents === "none".

Fix

• image-preview.css: closed content takes no pointer events, and body takes pointer events again as soon as the close starts. The flight looks the same.
• Image open now ships Smooth (0.3 s, bounce 0). motionTuning.spring takes an optional shipped preset. The Motion strip now shows Shipped, Snappy, Smooth and Calm, so every preset stays selectable.

Tests

• New packages/app/component-tests/image-preview.spec.ts. It closes the preview by Esc, by a backdrop click, by the close button, and mid-flight, then clicks the page straight away with a raw click. All four tests fail on beta and pass here.
• motion-tuning.test.ts covers a spring that ships a named preset.