feat(registry): add maps section with 4 new map blocks + docs

New blocks: world-map (D3 Natural Earth choropleth), us-map-bubble
(proportional city markers), us-map-hex (hexagonal tile grid),
us-map-flow (animated connection arcs between cities).

All blocks share the same dark theme and are composable — layer
bubble or flow on top of the choropleth via track indexes.

Adds "Maps" section to the catalog docs with MDX pages for all 5
map blocks (including the us-map from the previous commit).

registry/registry.json

@@ -43,6 +43,22 @@
       "name": "us-map",
       "type": "hyperframes:block"
     },
+    {
+      "name": "us-map-bubble",
+      "type": "hyperframes:block"
+    },
+    {
+      "name": "us-map-hex",
+      "type": "hyperframes:block"
+    },
+    {
+      "name": "us-map-flow",
+      "type": "hyperframes:block"
+    },
+    {
+      "name": "world-map",
+      "type": "hyperframes:block"
+    },
     {
       "name": "flowchart",
       "type": "hyperframes:block"