feat(registry): add vignette CSS component

Pure-CSS radial darkening overlay that fills its positioned parent and
pulls focus toward the center. Shape, size, and color are exposed as
CSS custom properties (--vignette-shape, --vignette-size,
--vignette-edge, --vignette-color), so a GSAP timeline can animate any
of them — the snippet's header comment shows the pattern for fading
the vignette in.

The Components section currently has four entries; this fills the
cinematic-cinematography gap a video editor expects out of the box
without bundling any asset (the effect is a single radial-gradient).
Default z-index 90 sits below grain-overlay (100) so grain reads on
top of the darkened corners.

Catalog page, registry index, and nav are regenerated via
scripts/generate-catalog-pages.ts.

registry/registry.json

@@ -63,6 +63,10 @@
       "name": "texture-mask-text",
       "type": "hyperframes:component"
     },
+    {
+      "name": "vignette",
+      "type": "hyperframes:component"
+    },
     {
       "name": "instagram-follow",
       "type": "hyperframes:block"