fix(registry): animate mk card offsets with transforms, not top/left

mk-background and mk-clone-wall-transition tween the card's `top`/`left`.
Layout properties snap to integer device pixels, so the move stutters under
the seek-by-frame capture engine (lint: gsap_non_transform_motion). Both
cards sit at top:0/left:0 in CSS, so the values carry straight over to x/y,
and in clone-wall the later scale composes cleanly with the translate.
Re-rendered both and diffed frames against the previous output — identical,
as intended: this changes how the motion is computed, not how it looks.

Adds scripts/lint-registry-items.mjs (bun run lint:registry-items), which
mounts each item into a throwaway project and lints it. Registry items ship
as `<name>.html`, so `hyperframes lint <dir>` fails with "No composition
found" and these items had never actually been linted — which is how both
errors reached main. Verified the script reproduces the original failure on
the pre-fix source.

Left as a local command rather than a CI gate for now; wiring it up needs
two prior fixes, noted in the PR.

registry/blocks/mk-clone-wall-transition/mk-clone-wall-transition.html

@@ -182,13 +182,16 @@
         /* The wall sits in place from t=0, fully hidden beneath the
            full-bleed card — the card's shrink IS the wall's reveal. */
 
-        /* 0.2–0.95  outgoing frame shrinks to a rounded card on the wall */
+        /* 0.2–0.95  outgoing frame shrinks to a rounded card on the wall.
+           x/y rather than left/top — layout properties snap to integer device
+           pixels under seek-by-frame capture. Base is top:0/left:0, so the
+           values carry over unchanged, and the later scale composes cleanly. */
         if (CONFIG.card.enabled) {
           tl.to(
             card,
             {
-              top: 330,
-              left: 640,
+              y: 330,
+              x: 640,
               width: 640,
               height: 420,
               borderRadius: 40,