Add per-circuit distance radius support (near: {lat, lon, miles})

Prep for a new circuit that should only show events within 500 miles
of St. Louis, MO — the ID given (OlkMrRfxrN) 404s against the leagues
endpoint (every other circuit ID is 12 chars, this one is 10, so it's
likely missing characters from a copy/paste), so adding the actual
circuit entry once that's confirmed. This part is independent and
verified against known distances (Collinsville IL ~10mi, Ashland MO
~111mi, PA ~748mi from St. Louis) — a no-op for every existing circuit
since `near` is optional and withinRadius() passes everything through
when it's unset.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SBzcNkW7JcYipnAX6HfgmK

sites/events/src/main.js

@@ -41,6 +41,12 @@ loadHTML('/footer.html', 'footer');
    entries here; the page builds one section per circuit.
    `id` is the leagueId from a circuit's BCP calendar URL,
    e.g. bestcoastpairings.com/circuit/<id>/calendar
+
+   Optional `near: { lat, lon, miles }` restricts a circuit to only
+   events within that radius (great-circle distance) — a fixed
+   property of the circuit itself, unlike the Format/Scope toggles
+   which the viewer controls. Events with no coordinate data are
+   excluded rather than assumed to be in range.
    ============================================================ */
 const CONFIG = {
   circuits: [
@@ -51,6 +57,27 @@ const CONFIG = {
   ],
 };
 
+// St. Louis, MO — reference point for circuits restricted by distance.
+const ST_LOUIS = { lat: 38.6270, lon: -90.1994 };
+
+// Great-circle distance in miles between two lat/lon points (haversine).
+function milesBetween(lat1, lon1, lat2, lon2) {
+  const R = 3958.8;
+  const toRad = d => (d * Math.PI) / 180;
+  const dLat = toRad(lat2 - lat1);
+  const dLon = toRad(lon2 - lon1);
+  const a = Math.sin(dLat / 2) ** 2 + Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) * Math.sin(dLon / 2) ** 2;
+  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
+}
+
+function withinRadius(ev, near) {
+  if (!near) return true;
+  const coord = ev.coordinate; // BCP gives [lon, lat]
+  if (!Array.isArray(coord) || coord.length !== 2) return false;
+  const [lon, lat] = coord;
+  return milesBetween(lat, lon, near.lat, near.lon) <= near.miles;
+}
+
 /* ---- BCP API ---- */
 const API = "https://newprod-api.bestcoastpairings.com/v1";
 const HEADERS = { "client-id": "web-app", "env": "bcp", "accept": "application/json" };
@@ -265,7 +292,8 @@ async function load() {
   allResults = await Promise.all(
     CONFIG.circuits.map(async circuit => {
       try {
-        return { circuit, events: await fetchUpcomingEvents(circuit.id) };
+        const events = await fetchUpcomingEvents(circuit.id);
+        return { circuit, events: events.filter(ev => withinRadius(ev, circuit.near)) };
       } catch (err) {
         console.error("Failed to load circuit", circuit.id, err);
         return { circuit, events: [], error: true };