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the same unpublished .html path, so it would have shown an empty frame.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/grain-overlay.mdx

@@ -3,6 +3,8 @@ title: "Grain Overlay"
 description: "Animated film grain texture overlay using CSS keyframes — adds warmth and analog character to any composition"
 ---
 
+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="grain-overlay preview"
@@ -12,19 +14,97 @@ description: "Animated film grain texture overlay using CSS keyframes — adds w
 
 ## Install
 
-```bash Terminal
-npx hyperframes add grain-overlay
-```
+<InstallCommand command="npx hyperframes add grain-overlay" />
 
 That writes one file: `compositions/components/grain-overlay.html`.
 
-## Paste it into your composition
+## Source
 
-Open `compositions/components/grain-overlay.html` and copy what is inside into your own composition.
-The file opens with a comment header that walks you through it.
+<Accordion title={`grain-overlay.html`}>
 
-A component has no size or duration of its own. It takes both from the composition
-you paste it into.
+```html
+<!--
+  Grain Overlay — animated film grain texture.
+
+  Usage: paste this snippet into your composition's HTML.
+  The overlay covers the full viewport with pointer-events: none
+  so it sits on top of all content without blocking interaction.
+
+  Customize:
+  - opacity: adjust .grain-texture opacity (default 0.15)
+  - speed: change animation duration (default 0.5s)
+  - texture: swap the background URL for a different pattern
+  - z-index: adjust #grain-overlay z-index to layer correctly
+-->
+
+<div
+  id="grain-overlay"
+  style="
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    pointer-events: none;
+    z-index: 100;
+  "
+>
+  <div class="grain-texture"></div>
+</div>
+
+<style>
+  @keyframes hf-grain-noise {
+    0%,
+    100% {
+      transform: translate(0, 0);
+    }
+    10% {
+      transform: translate(-5%, -5%);
+    }
+    20% {
+      transform: translate(-10%, 5%);
+    }
+    30% {
+      transform: translate(5%, -10%);
+    }
+    40% {
+      transform: translate(-5%, 15%);
+    }
+    50% {
+      transform: translate(-10%, 5%);
+    }
+    60% {
+      transform: translate(15%, 0);
+    }
+    70% {
+      transform: translate(0, 10%);
+    }
+    80% {
+      transform: translate(-15%, 0);
+    }
+    90% {
+      transform: translate(10%, 5%);
+    }
+  }
+
+  #grain-overlay .grain-texture {
+    position: absolute;
+    top: -50%;
+    left: -50%;
+    width: 200%;
+    height: 200%;
+    background: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise)'/%3E%3C/svg%3E");
+    opacity: 0.15;
+    animation: hf-grain-noise 0.5s steps(1) infinite;
+  }
+</style>
+```
+
+</Accordion>
+
+## Usage
+
+Open `compositions/components/grain-overlay.html` and paste its contents into your composition. See the comment header in the file for detailed instructions.
 
 {/* hf:generated-footer */}