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/telemetry/health.server.ts

@@ -0,0 +1,56 @@
+export interface HealthChecks {
+  pocketbase: "ok" | "down";
+  supertokens: "ok" | "down";
+}
+
+export interface HealthSnapshot {
+  status: "ok" | "degraded";
+  checks: HealthChecks;
+  checkedAt: string;
+}
+
+const CHECK_TTL_MS = 10_000;
+const CHECK_TIMEOUT_MS = 2_000;
+
+let cached: HealthSnapshot | null = null;
+let refreshing: Promise<HealthSnapshot> | null = null;
+
+const ping = async (url: string): Promise<boolean> => {
+  try {
+    const response = await fetch(url, { signal: AbortSignal.timeout(CHECK_TIMEOUT_MS) });
+    return response.ok;
+  } catch {
+    return false;
+  }
+};
+
+const runChecks = async (): Promise<HealthSnapshot> => {
+  const [pocketbase, supertokens] = await Promise.all([
+    ping(`${process.env.POCKETBASE_URL}/api/health`),
+    ping(`${process.env.SUPERTOKENS_URI}/hello`),
+  ]);
+
+  cached = {
+    status: pocketbase && supertokens ? "ok" : "degraded",
+    checks: {
+      pocketbase: pocketbase ? "ok" : "down",
+      supertokens: supertokens ? "ok" : "down",
+    },
+    checkedAt: new Date().toISOString(),
+  };
+  return cached;
+};
+
+// Stale-while-revalidate: k8s probes get the cached snapshot instantly while a
+// refresh runs in the background; only the very first request awaits a check.
+export const getHealthSnapshot = async (): Promise<HealthSnapshot> => {
+  if (cached && Date.now() - Date.parse(cached.checkedAt) < CHECK_TTL_MS) {
+    return cached;
+  }
+  if (!refreshing) {
+    refreshing = runChecks().finally(() => {
+      refreshing = null;
+    });
+  }
+  return cached ?? refreshing;
+};