fix(web): support multiple gateway tabs by reducing SSE connections

Each browser tab opened 2 SSE connections (chat events + log events).
With the HTTP/1.1 per-origin limit of 6, the 3rd tab exhausted the
pool and couldn't load any data.

Three changes:

1. Lazy log SSE — only connect when the logs tab is active, disconnect
   when switching away. Most users rarely view logs, so this saves a
   connection slot per tab.

2. Visibility API — close SSE when the browser tab goes to background
   (user switches to another tab), reconnect when it becomes visible.
   Background tabs don't need real-time events.

3. Combined with the existing beforeunload cleanup, this means:
   - Active foreground tab: 1 connection (chat SSE only, +1 if logs tab)
   - Background tabs: 0 connections
   - Closed/refreshed tabs: 0 connections (beforeunload cleanup)

This allows many gateway tabs to coexist within the 6-connection limit.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

src/channels/web/static/app.js

@@ -184,7 +184,7 @@ function authenticate() {
       cleaned.searchParams.delete('log_level');
       window.history.replaceState({}, '', cleaned.pathname + cleaned.search);
       connectSSE();
-      connectLogSSE();
+      // Log SSE is connected lazily when the logs tab is opened (saves a connection slot).
       startGatewayStatusPolling();
       checkTeeStatus();
       loadThreads();
@@ -223,6 +223,20 @@ window.addEventListener('beforeunload', () => {
   if (logEventSource) { logEventSource.close(); logEventSource = null; }
 });
 
+// Pause SSE when the browser tab is hidden (another tab is focused) and resume
+// when it becomes visible again. This frees connection slots for other tabs
+// running the gateway — without this, each tab holds 1-2 SSE connections and
+// the 3rd tab exhausts the browser's per-origin limit.
+document.addEventListener('visibilitychange', () => {
+  if (document.hidden) {
+    if (eventSource) { eventSource.close(); eventSource = null; }
+    if (logEventSource) { logEventSource.close(); logEventSource = null; }
+  } else if (token) {
+    connectSSE();
+    if (currentTab === 'logs') connectLogSSE();
+  }
+});
+
 // Note: main event listener registration is at the bottom of this file (search
 // "Event Listener Registration"). Do NOT add duplicate listeners here.
 
@@ -2222,7 +2236,8 @@ function switchTab(tab) {
   if (tab === 'jobs') loadJobs();
   if (tab === 'missions') loadMissions();
   if (tab === 'routines') loadRoutines();
-  if (tab === 'logs') applyLogFilters();
+  if (tab === 'logs') { connectLogSSE(); applyLogFilters(); }
+  else if (logEventSource) { logEventSource.close(); logEventSource = null; }
   if (tab === 'settings') {
     loadSettingsSubtab(currentSettingsSubtab);
   } else {