Adds frontend implementation for feature discovery notifications:
- Polls /api/help/notifications every 30 seconds
- Displays notification cards with slide-in animation
- Handles action button clicks for navigation
- Persists dismissed notifications to prevent re-display
- Auto-dismisses after 30 seconds
Completes the feature discovery notifications feature for Phase 9,
complementing the backend notifier and monitor implementations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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