fix: add buffer_overflows_total metric increment

The metric was defined but never incremented when buffer overflow occurred.

Added recordBufferOverflow() function and call it from checkBufferOverflow()
when buffer exceeds maxBufferSize (default 5000 events).

src/Utils/event-buffer.ts

@@ -449,6 +449,10 @@ export const makeEventBuffer = (
 				currentSize: currentEventCount,
 				maxSize: config.maxBufferSize
 			})
+			// Record overflow metric
+			if (metricsModule) {
+				metricsModule.recordBufferOverflow()
+			}
 			flush(true)
 			return true
 		}

src/Utils/prometheus-metrics.ts

@@ -1910,6 +1910,18 @@ export function recordCacheCleanup(removedCount: number): void {
 	}
 }
 
+/**
+ * Record a buffer overflow event
+ * Used by event-buffer.ts when buffer exceeds max size
+ */
+export function recordBufferOverflow(): void {
+	try {
+		metrics.bufferOverflows?.inc({ type: 'event' })
+	} catch {
+		// Metrics not initialized, ignore silently
+	}
+}
+
 // ============================================
 // Global Instance
 // ============================================