[codex] Add embedded DCI simulation backend

[diputs18]

Summary

• Add an embedded background simulation backend for serve mode so DCI nodes can continuously heartbeat, pull leases, and report task results.
• Add a 24-node DCI runtime topology inventory and wire it into the example config.
• Update Windows start/restart scripts to launch with the embedded simulation backend by default.

Validation

• python -m py_compile src\tianjun\node_agent\clients.py src\tianjun\simulation\backend.py src\tianjun\cli.py
• Verified a live simulation task targeting dci-dc1-hangzhou-vm-1 completed and produced an execution record.