[deploy] systemd unit for agent + bridge on Jetson

[jdev-02]

Owner: Kyle (P3)
Done: systemd framework + auto-update infra (PR #88, #92) for the planner.

Remaining acceptance:

• Decide: is tera-planner.service the canonical agent service, or do we
  add tera-agent.service for agent.app:app on a separate port?
• If the latter: clone tera-planner.service to tera-agent.service,
  ExecStart=uvicorn agent.app:app --port 8000, Environment=
  TERA_PHASE=3 OLLAMA_MODEL=gemma3:4b TERA_DEVICE_PROFILE=austere (mirrors [deploy] Start TERA agent on Jetson with OLLAMA_MODEL=gemma3:4b #82).
• Add tera-bridge.service once [atak] Signed CoT bridge over multicast #13/[routing] Merge ben/valhalla-local-sf — Valhalla + OSM/DEM scripts + KML emit #83 lands the bridge code.

Tracker: #82 covers the runtime smoke-test for the agent service once it has
a unit file.

[kylemhicks]

Status after PR #98/#101/#103: the demo runtime is now the Docker Compose Source Planner service on port 8080 plus host Ollama startup/warmup. We have not added a separate tera-agent.service for agent.app:app on port 8000, and no bridge service should be added unless the team resurrects the Python bridge. Keep this open as the systemd/post-MVP service decision tracker.