Add real-time OTA update progress broadcasting to dashboard clients:
- Hub.BroadcastOTAProgress() sends progress updates over WebSocket
- OTA Manager now broadcasts state transitions: pending → downloading → rebooting → verified/failed/rollback
- Dashboard can show live OTA status per node during fleet updates
- Includes test suite for fleet page functionality
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
