docs(atak): add demo-day playbook for jetson-compose-refresh

[jdev-02]

Why

PR #92 lands the `make jetson-compose-refresh` target and the script behind it. Right now only Kyle knows the recipe (where to run it, what envs to set, how it interacts with the existing systemd autoupdate path). For demo day we want anyone on the team to be able to push the latest `main` to the Jetson if Kyle is unavailable.

What

Adds a "Demo-Day Playbook" section to the top of `atak/README.md`:

• The single command (after first-time setup):
  ```
  make jetson-compose-refresh
  ```
• The 5-step internal flow that target runs (pull → stop systemd → `docker compose down/up` → curl smoke-test against `atakAgentBtn`).
• Env-var overrides table (`REPO_DIR`, `BRANCH`, `SERVICE_NAME`, `PLANNER_URL`, ...).
• The `.env` template the compose service reads on the Jetson (`OLLAMA_`, `ANTHROPIC_API_KEY`, `CESIUM_ION_TOKEN`, `TERA_ATAK_`).
• A short "two refresh paths" subsection clarifying that we now have two ways to keep the Jetson current — native systemd autoupdate vs Docker compose refresh — and you should pick one (port 8080 conflict otherwise). Recommends the Docker path for the hackathon demo.

The original Jetson Setup, ATAK Device Setup, and Troubleshooting sections are untouched.

Depends on

• chore(deploy): add Jetson compose refresh script #92 — introduces `make jetson-compose-refresh` and `deploy/scripts/jetson_compose_refresh.sh` that this playbook documents. Merge order should be: chore(deploy): add Jetson compose refresh script #92 first, then this.

Test

• `mdformat`-clean (no linter errors).
• All commands in the playbook are direct copies from chore(deploy): add Jetson compose refresh script #92's script defaults; no extra moving parts introduced here.