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.

templates/static/main.js

@@ -1,3 +1,6 @@
+const CFGEO_ENDPOINT = "https://cfgeo.abdusco.workers.dev/";
+const CFGEO_TIMEOUT_MS = 2000;
+
 const app = () => ({
     futureTimes: [],
     selectedLocation: Alpine.$persist(null),
@@ -34,13 +37,30 @@ const app = () => ({
         }, 500);
 
         if (!urlCoords) {
-            try {
-                const coords = await getUserLocation();
-                await this.selectNearestLocation(coords.latitude, coords.longitude, {updateURL: true});
-            } catch (_error) {
-                // Ignore geolocation errors and rely on manual search.
+            await this.resolveDefaultLocation();
+        }
+    },
+
+    async resolveDefaultLocation() {
+        let browserResolved = false;
+        const geoPromise = getUserLocation()
+            .then((coords) => {
+                browserResolved = true;
+                return coords;
+            })
+            .catch(() => null);
+
+        if (!this.selectedLocation) {
+            const cfCoords = await withTimeout(getCFGeoLocation(), CFGEO_TIMEOUT_MS);
+            if (cfCoords && !browserResolved) {
+                await this.selectNearestLocation(cfCoords.latitude, cfCoords.longitude, {updateURL: false});
             }
         }
+
+        const geoCoords = await geoPromise;
+        if (geoCoords) {
+            await this.selectNearestLocation(geoCoords.latitude, geoCoords.longitude, {updateURL: true});
+        }
     },
 
     onHash() {
@@ -396,6 +416,26 @@ function getUserLocation() {
     });
 }
 
+async function getCFGeoLocation() {
+    if (!CFGEO_ENDPOINT) {
+        return null;
+    }
+
+    const data = await fetchJSON(CFGEO_ENDPOINT);
+    if (typeof data.latitude !== "number" || typeof data.longitude !== "number") {
+        return null;
+    }
+
+    return {latitude: data.latitude, longitude: data.longitude};
+}
+
+function withTimeout(promise, ms) {
+    return Promise.race([
+        promise,
+        new Promise((resolve) => setTimeout(() => resolve(null), ms))
+    ]).catch(() => null);
+}
+
 function normalizeLanguageTag(tag) {
     return String(tag).toLowerCase().split("-")[0];
 }