feat(web): Add Cloudflare Workers geolocation fallback

Add a minimal cfgeo Cloudflare Worker that returns coarse location
from Cloudflare's edge geolocation data. Use it as a fast default
location on load, preferring browser geolocation or an explicit
search/URL selection whenever those are available.

cfgeo/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "cfgeo",
+  "private": true,
+  "scripts": {
+    "dev": "wrangler dev",
+    "deploy": "wrangler deploy"
+  },
+  "devDependencies": {
+    "wrangler": "^3.90.0"
+  }
+}