fix: close SSE connection cleanly on page navigation

beforeunload closes the EventSource explicitly so the browser doesn't
log "connection interrupted while page was loading". onerror handler
suppresses auto-reconnect noise if the connection temporarily drops.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/static/app.js

@@ -1080,6 +1080,13 @@
         // ── Real-time Talk updates (SSE) ─────────────────────────────
         const evtSource = new EventSource('/events');
 
+        // Close cleanly on navigation so the browser doesn't log "connection interrupted"
+        window.addEventListener('beforeunload', () => evtSource.close());
+
+        evtSource.onerror = () => {
+            // EventSource auto-reconnects — nothing to do; suppress console noise
+        };
+
         evtSource.onmessage = (e) => {
             let data;
             try { data = JSON.parse(e.data); } catch { return; }