lint: flag CSS transition (seek-unsafe; adapter only covers @keyframes) #3493

Problem

CSS transition runs on the browser clock. A GSAP class/attr swap looks correct in preview and --workers 1. Parallel chunk workers (and snapshot --at past the settle time) restore the class on a fresh page, so the browser restarts the fade and the export flashes.

Motion skills already ban it. The CSS adapter only discovers animation-name — finite @keyframes are seekable; transition is not. hyperframes check does not flag it. Agents and web-CSS habits keep producing it.

Proposed solution

A lint error (so check fails, same family as non_deterministic_code / gsap_infinite_repeat):

• Flag transition / transition-* (and -webkit-) in <style> and inline style="".
• Allow transition: none / transition-property: none.
• Ignore custom properties (--transition-speed).
• Fix hint: keep the class swap for state; put the visual change on the paused GSAP timeline.

The frame-worker self-check already uses the label css_transition_used — reuse that code name if you add the rule.

Alternatives considered

finish() jump-spawned CSS transitions in the renderer. That papers over illegal motion and still leaves agents producing it.

Additional context

Fixture: https://github.com/ArcadeHQ/hyperframes-repros/tree/patch/jump-seek-css-settle

(check is clean; --workers 4 and snapshot --at 2 replay the 0.5s fade.)