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/src/index.js

@@ -0,0 +1,23 @@
+export default {
+    async fetch(request) {
+        const cf = request.cf || {};
+
+        const body = {
+            latitude: cf.latitude ? Number(cf.latitude) : null,
+            longitude: cf.longitude ? Number(cf.longitude) : null,
+            city: cf.city ?? null,
+            region: cf.region ?? null,
+            country: cf.country ?? null,
+            timezone: cf.timezone ?? null,
+            postalCode: cf.postalCode ?? null,
+        };
+
+        return new Response(JSON.stringify(body), {
+            headers: {
+                'content-type': 'application/json',
+                'access-control-allow-origin': '*',
+                'cache-control': 'no-store',
+            },
+        });
+    },
+};