feat: add consistent deployment/update process (deploy.sh + docs + AGENTS.md)

- scripts/deploy.sh: target-aware deploy (dankclaw/dankserver). Pushes main,
  pulls on the target, installs/enables systemd unit, restarts service, and
  checks the health endpoint; --dry-run preview; pre-flight dirty-tree check
- docs/deployment.md: full deployment/update process with mermaid workflow,
  target map, manual update commands, service units, and troubleshooting
- AGENTS.md: add Deployment & Update Process section (deploy.sh usage, target
  map, mermaid workflow) and a Summary table row
- docs/index.md: crosslink deployment doc

docs/index.md

@@ -35,6 +35,7 @@ graph LR
 
 - [[VLLM Overview]] — installation, CLI, API, architecture, quantization, parallelism
 - [[VLLM Index]] — quick reference with commands, endpoints, and parameter table
+- [[deployment]] — deploy and update process for both servers
 
 ## Memory Management