feat(telemetry): rollups, alerts, scheduler, health checks, admin server fns

- pure rollup accumulators with tests; daily upserts keyed date/metric/dim
- alert checks with db-backed cooldown and push to admin players
- in-process scheduler started from health probes
- health endpoint checks pb + supertokens, stale-while-revalidate, always 200
- sse connection counter moved to emitter
- telemetry feature server fns: events/errors/groups/rollups/alerts/status

src/lib/events/emitter.ts

@@ -68,6 +68,20 @@ export const emitServerEvent = (event: ServerEvent) => {
   serverEvents.emit(event.type, event);
 };
 
+let activeConnections = 0;
+
+export const incrementConnections = () => {
+  activeConnections++;
+  return activeConnections;
+};
+
+export const decrementConnections = () => {
+  activeConnections = Math.max(0, activeConnections - 1);
+  return activeConnections;
+};
+
+export const getActiveConnectionCount = () => activeConnections;
+
 if (process.env.NODE_ENV === 'development') {
   setInterval(() => {
     const listenerCounts = Object.fromEntries(