fix: use environment variables for TS_AUTHKEY and TS_LOGIN_SERVER

- docker-compose.yml: TS_AUTHKEY and TS_LOGIN_SERVER now read from environment
- README.md: updated Tailscale configuration instructions to reference env vars instead of editing the file
- Added .gitignore to prevent committing secrets or Tailscale state

This protects reusable test auth keys and custom coordination servers from being committed to any ts-* repo.

README.md

@@ -33,7 +33,7 @@ ts-{{service}}/
     mkdir -p tailscale/tailscale-data
     ```
 3. Configure Tailscale
-    - Replace `{{YOUR_TAILSCALE_AUTHKEY}}` in the docker-compose.yml with your actual Tailscale auth key
+    - Make sure `TS_AUTHKEY` and `TS_LOGIN_SERVER` are set in your environment (or a local `.env` file) before running docker compose.
     - Optionally, update the file in `tailscale/config/serve.json` if you need specific Tailscale serve configurations
         - CAUTION: Changing `"${TS_CERT_DOMAIN}:443": false` to `true` will expose the service to the internet