fix(storm-intel): call IEM API directly from browser — no proxy needed

IEM geojson/sbw.geojson has CORS open to all origins so the browser can
fetch it directly. Moves all transformation logic into useStormEvents.js,
eliminating the need for vercel dev or any server-side proxy. Works with
plain pnpm run dev on localhost. Falls back to MOCK_STORM_EVENTS if IEM
is unreachable. api/storm-polygons.js kept as optional edge cache layer.

vercel.json

@@ -1,6 +1,9 @@
 {
+  "buildCommand": "pnpm build",
+  "devCommand": "pnpm dev",
+  "outputDirectory": "dist",
   "rewrites": [
-    { "source": "/api/(.*)", "destination": "/api/$1" },
-    { "source": "/(.*)", "destination": "/index.html" }
+    { "source": "/((?!api/).*)", "destination": "/index.html" }
   ]
 }
+