fix: prevent sync banner from flashing on session switches

Added isFirstConnectRef to distinguish between first SSE connection
(page load) and subsequent reconnects (session switches). Only the
first connection forces the banner to show; subsequent connects use
non-forced mode which only displays the banner when returning from
background within 30s, eliminating unwanted banner flashes on
session changes.

web/src/App.tsx

@@ -88,11 +88,21 @@ export function App() {
     const selectedSessionId = sessionMatch ? sessionMatch.sessionId : null
     const { isSyncing, startSync, endSync } = useSyncingState()
     const syncTokenRef = useRef(0)
+    const isFirstConnectRef = useRef(true)
 
     const handleSseConnect = useCallback(() => {
         // Increment token to track this specific connection
         const token = ++syncTokenRef.current
-        startSync({ force: true })
+
+        // Only force show banner on first connect (page load)
+        // Subsequent connects (session switches) use non-forced mode
+        // which only shows banner when returning from background
+        if (isFirstConnectRef.current) {
+            isFirstConnectRef.current = false
+            startSync({ force: true })
+        } else {
+            startSync()
+        }
         const invalidations = [
             queryClient.invalidateQueries({ queryKey: queryKeys.sessions }),
             ...(selectedSessionId ? [