Add 8 custom metric instruments using OTel proxy meter

src/observability/metrics/custom.ts

@@ -0,0 +1,32 @@
+import { metrics } from "@opentelemetry/api";
+
+/**
+ * Module-level metric instruments for the flights remote component.
+ * Safe to declare at module scope — @opentelemetry/api's proxy meter
+ * lazy-resolves to the real MeterProvider after initServerOtel/initBrowserOtel runs.
+ */
+const meter = metrics.getMeter("flights");
+
+/** SSR request duration histogram (seconds). */
+export const flightsSsrRequestDuration = meter.createHistogram("flights.ssr.request.duration");
+
+/** Upstream API request duration histogram (seconds). */
+export const flightsApiRequestDuration = meter.createHistogram("flights.api.request.duration");
+
+/** Upstream API error counter (by route, status). */
+export const flightsApiError = meter.createCounter("flights.api.error");
+
+/** SignalR active connections gauge. */
+export const flightsSignalRConnected = meter.createUpDownCounter("flights.signalr.connected");
+
+/** SignalR messages received counter. */
+export const flightsSignalRMessageReceived = meter.createCounter("flights.signalr.message.received");
+
+/** SignalR disconnection counter (by reason). */
+export const flightsSignalRDisconnect = meter.createCounter("flights.signalr.disconnect");
+
+/** Feature component render counter (by feature name). */
+export const flightsFeatureRender = meter.createCounter("flights.feature.render");
+
+/** Unhandled React error counter (caught by ErrorBoundary). */
+export const flightsReactError = meter.createCounter("flights.react.error");