fix(metrics): clear startPromise on stop() to allow restart

FIX: startPromise was never cleared after stop(), causing start()
to return the old resolved promise instead of creating a new server.

This broke any flow that stops and restarts metrics (config reloads, tests).

Now stop() clears startPromise, allowing proper server restart.

src/Utils/prometheus-metrics.ts

@@ -1133,9 +1133,13 @@ export class MetricsServer {
 
 	/**
 	 * Stop the metrics HTTP server
+	 * FIX: Clears startPromise to allow restart after stop
 	 */
 	stop(): Promise<void> {
 		return new Promise((resolve) => {
+			// FIX: Clear cached promise so start() can be called again
+			this.startPromise = null
+
 			if (this.collectInterval) {
 				clearInterval(this.collectInterval)
 				this.collectInterval = null