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the same unpublished .html path, so it would have shown an empty frame.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.

registry/components/beat-pulse-background/registry-item.json

@@ -0,0 +1,54 @@
+{
+  "$schema": "https://hyperframes.heygen.com/schema/registry-item.json",
+  "name": "beat-pulse-background",
+  "type": "hyperframes:component",
+  "title": "Beat Pulse Background",
+  "description": "An accent-derived backdrop pulses its glow intensity and saturation on a deterministic, supplied beat grid.",
+  "tags": ["motion-primitive", "background", "beat", "pulse", "rhythmic", "reactive"],
+  "jobs": ["emphasize"],
+  "family": "backgrounds",
+  "profile": "rhythmic",
+  "evidence": "Wave G U21 beat-pulse-background specification",
+  "files": [
+    {
+      "path": "beat-pulse-background.html",
+      "target": "compositions/components/beat-pulse-background.html",
+      "type": "hyperframes:snippet"
+    }
+  ],
+  "variables": [
+    {
+      "id": "beats",
+      "type": "string",
+      "role": "timing",
+      "label": "Beats",
+      "description": "Comma-separated beat times in seconds. Invalid entries are ignored and numeric values are clamped to the composition duration.",
+      "default": "0.5,1.0,1.5,2.0,2.5,3.0,3.5"
+    },
+    {
+      "id": "accent",
+      "type": "enum",
+      "role": "style",
+      "label": "Accent",
+      "description": "Accent token family used by the pulsing glow.",
+      "default": "green",
+      "options": [
+        { "value": "green", "label": "Green" },
+        { "value": "blue", "label": "Blue" },
+        { "value": "violet", "label": "Violet" }
+      ]
+    },
+    {
+      "id": "intensity",
+      "type": "enum",
+      "role": "style",
+      "label": "Intensity",
+      "description": "Strength of the glow and saturation pulse.",
+      "default": "subtle",
+      "options": [
+        { "value": "subtle", "label": "Subtle" },
+        { "value": "club", "label": "Club" }
+      ]
+    }
+  ]
+}