fix(toast): sticky toasts + improve update notification visibility (P5-40)

Add sticky?: boolean to ToastNotif — sticky toasts skip the 4s auto-dismiss
timer entirely, staying until the user clicks or manually dismisses. Sticky
toasts also use cyan accent/glow (vs orange for messages) and allow the body
to wrap rather than truncate, so longer action-oriented copy is fully readable.

Update the Tauri update toast to: sticky: true, ⬆ prefix on the title,
"Click to install and restart" as explicit call to action.

Fixes: auto-dismiss before user noticed it, no visual distinction from
a regular message notification.

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

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -459,11 +459,12 @@ function TauriUpdateFeature() {
     firedRef.current = status.version;
     setToast({
       id: `tauri-update-${status.version}`,
-      displayName: 'Update Available',
-      body: `Lotus Chat ${status.version} is ready to install.`,
+      displayName: '⬆ Update Available',
+      body: `Lotus Chat ${status.version} is ready. Click to install and restart.`,
       roomName: 'System',
       roomId: '',
       onClick: install,
+      sticky: true,
     });
   }, [status, setToast, install]);