Add comprehensive capability routing system to scheduler hub:
- Capability-aware worker matching with requirement/offer negotiation
- Hub v2 protocol with structured message types and heartbeat management
- Worker capability advertisement and dynamic routing decisions
- Orphan recovery for disconnected workers with state reconciliation
- Template-based job scheduling with capability constraints
Add extensive test coverage:
- Unit tests for capability routing logic and heartbeat mechanics
- Unit tests for orphan recovery scenarios
- E2E tests for capability routing across multiple workers
- Hub capabilities integration tests
- Scheduler fixture helpers for test setup
Protocol improvements:
- Define structured protocol messages for hub-worker communication
- Add capability matching algorithm with scoring
- Implement graceful worker disconnection handling
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