feat(registry): add us-map choropleth block

Animated US population density choropleth using D3 geoAlbersUsa
projection with TopoJSON. Includes staggered state reveals, label
fade-ins, gradient legend, and highlight pulses on densest states.

registry/blocks/us-map/registry-item.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "https://hyperframes.heygen.com/schema/registry-item.json",
+  "name": "us-map",
+  "type": "hyperframes:block",
+  "title": "US Map",
+  "description": "Animated US choropleth map with staggered state reveals, value labels, and gradient legend — pure inline SVG with GSAP",
+  "tags": ["data", "map", "geography", "usa", "choropleth"],
+  "dimensions": {
+    "width": 1920,
+    "height": 1080
+  },
+  "duration": 12,
+  "files": [
+    {
+      "path": "us-map.html",
+      "target": "compositions/us-map.html",
+      "type": "hyperframes:composition"
+    }
+  ]
+}