Simplify embedded mode navigation to stay within iframe

Remove the complex token-passing logic for new tabs in embedded mode.
Instead, navigation now stays within the iframe for a simpler UX.

- Remove handleNewWindowClick auth handler from sidebar items
- Simplify useNewWindow hook to navigate within iframe when embedded

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/Automations.tsx

@@ -1,7 +1,7 @@
 import { useState, useEffect, useRef, useCallback } from 'react';
 import { useTranslation } from 'react-i18next';
 import { useQuery } from '@tanstack/react-query';
-import { Bot, RefreshCw, AlertTriangle, Loader2, Sparkles, RotateCcw, ChevronDown } from 'lucide-react';
+import { Bot, RefreshCw, AlertTriangle, Loader2, ExternalLink, Sparkles, RotateCcw, ChevronDown } from 'lucide-react';
 import api from '../api/client';
 import { usePlanFeatures } from '../hooks/usePlanFeatures';
 import { UpgradePrompt } from '../components/UpgradePrompt';