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/wrangler.toml

@@ -0,0 +1,3 @@
+name = "cfgeo"
+main = "src/index.js"
+compatibility_date = "2024-01-01"