feat(registry): bring back the video-primitive moves (#3169)

Restores the 208 catalog items reverted after their previews 404'd in
production, this time on the payload mechanism rather than the .html files
that caused the outage.

The generator no longer writes a preview document to docs/public. That writer,
and the machinery under it, existed only to produce files the docs host
discards, so it is gone rather than bypassed. Items now embed the composition
itself via a payload, which is what the previous change already does for the
items that were already in the catalog.

The variables explorer is parked, not restored: it drove its preview through
the same unpublished .html path, so it would have shown an empty frame. Items
that declare variables get the live player plus the static variables table, and
reconnecting the explorer to payloads is a follow-up.

docs/catalog/components/grid-pixelate-wipe.mdx

@@ -3,6 +3,8 @@ title: "Grid Pixelate Wipe"
 description: "Transition effect where the screen dissolves into a grid of squares that fade out with staggered timing — use between scenes"
 ---
 
+import { InstallCommand } from "/snippets/install-command.jsx";
+
 <iframe
   className="w-full aspect-video rounded-xl border-0 bg-zinc-100 dark:bg-zinc-800"
   title="grid-pixelate-wipe preview"
@@ -12,19 +14,102 @@ description: "Transition effect where the screen dissolves into a grid of square
 
 ## Install
 
-```bash Terminal
-npx hyperframes add grid-pixelate-wipe
-```
+<InstallCommand command="npx hyperframes add grid-pixelate-wipe" />
 
 That writes one file: `compositions/components/grid-pixelate-wipe.html`.
 
-## Paste it into your composition
+## Source
 
-Open `compositions/components/grid-pixelate-wipe.html` and copy what is inside into your own composition.
-The file opens with a comment header that walks you through it.
+<Accordion title={`grid-pixelate-wipe.html`}>
 
-A component has no size or duration of its own. It takes both from the composition
-you paste it into.
+```html
+<!--
+  Grid Pixelate Wipe — transition effect.
+
+  Usage: place this overlay in your composition. To transition between
+  scenes, animate .grid-cell scale from 0→1 (cover) then 1→0 (reveal)
+  using GSAP stagger with a "from" pattern.
+
+  Customize:
+  - COLS / ROWS: grid density (default 16×9), edit in the script below
+  - --grid-color: cell fill color (default black)
+  - Stagger "from": "center" for radial, "edges" for inward, "random" for scatter
+-->
+
+<div
+  id="grid-pixelate-overlay"
+  style="
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    pointer-events: none;
+    z-index: 999;
+    display: grid;
+  "
+></div>
+
+<style>
+  #grid-pixelate-overlay {
+    --grid-color: black;
+  }
+
+  #grid-pixelate-overlay .grid-cell {
+    background: var(--grid-color);
+    transform: scale(0);
+    transform-origin: center center;
+  }
+</style>
+
+<script>
+  (function () {
+    const COLS = 16;
+    const ROWS = 9;
+    const overlay = document.getElementById("grid-pixelate-overlay");
+    if (!overlay) return;
+
+    overlay.style.gridTemplateColumns = `repeat(${COLS}, 1fr)`;
+    overlay.style.gridTemplateRows = `repeat(${ROWS}, 1fr)`;
+
+    for (let i = 0; i < COLS * ROWS; i++) {
+      const cell = document.createElement("div");
+      cell.className = "grid-cell";
+      overlay.appendChild(cell);
+    }
+  })();
+</script>
+
+<!--
+  Timeline integration example:
+
+  // Cover screen with grid (transition out of scene A)
+  tl.to("#grid-pixelate-overlay .grid-cell", {
+    scale: 1,
+    duration: 0.6,
+    stagger: { amount: 0.6, from: "center" },
+    ease: "power2.inOut",
+  }, 3.0);
+
+  // Swap scene content at midpoint
+  tl.set("#scene-a", { opacity: 0 }, 3.6);
+  tl.set("#scene-b", { opacity: 1 }, 3.6);
+
+  // Reveal scene B by removing grid
+  tl.to("#grid-pixelate-overlay .grid-cell", {
+    scale: 0,
+    duration: 0.6,
+    stagger: { amount: 0.6, from: "edges" },
+    ease: "power2.inOut",
+  }, 3.6);
+-->
+```
+
+</Accordion>
+
+## Usage
+
+Open `compositions/components/grid-pixelate-wipe.html` and paste its contents into your composition. See the comment header in the file for detailed instructions.
 
 {/* hf:generated-footer */}