fix(web_ui): drop stale (max) suffix from xhigh effort label

xhigh and max are distinct reasoning-effort levels (see EFFORT_LEVELS
in events.rs); labelling xhigh as '(max)' implied they were the same
level, per issue #2258.

frontend/packages/agent/src/app.js

@@ -334,9 +334,11 @@ window.marked = marked;
       // Display-only labels for well-known levels; any level the backend
       // sends that isn't here just shows its bare name.
       const EFFORT_DESCRIPTIONS = {
+        low:    'low',
         medium: 'medium  (default)',
         high:   'high',
-        xhigh:  'xhigh   (max)',
+        xhigh:  'xhigh',
+        max:    'max',
       };
       for (const level of availableEfforts) {
         const label = EFFORT_DESCRIPTIONS[level] ?? level;