feat: Add context propagation, state sync, and tests
- Add context.Context to ManagerInterface methods (StartMiner, StopMiner, UninstallMiner)
- Add WebSocket state sync on client connect (sends current miner states)
- Add EventStateSync event type and SetStateProvider method
- Add manager lifecycle tests (idempotent stop, context cancellation, shutdown timeout)
- Add database tests (initialization, hashrate storage, stats)
- Add EventHub tests (creation, broadcast, client count, state provider)
- Update all test files for new context-aware API
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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