Add generic deployment docs and fix stale references

Adds docs/deployment.md, a platform-agnostic guide (any Linux host with
Docker) built around a git-pull based fast-redeploy workflow, replacing the
Proxmox-specific deploy/proxmox_llm_deploy.md which was also stale (old
`persona` field, single-shared-token model predating multi-user auth).

Also: drops the unused DAYBOOK_API_TOKEN from deploy/env.example, documents
the new DELETE endpoint and capabilities `methods` field in docs/api.md and
docs/agent_quickstart.md, and fixes CLAUDE.md's OpenCode note now that
opencode.json is untracked (machine-specific MCP config).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/agent_quickstart.md

@@ -124,6 +124,17 @@ Invoke-RestMethod `
   -Body $body
 ```
 
+## 8. Delete An Artifact
+
+```powershell
+Invoke-RestMethod `
+  -Uri "http://127.0.0.1:8001/api/artifacts/$($artifact.id)" `
+  -Method Delete `
+  -Headers @{ Authorization = "Bearer <your-personal-token>" }
+```
+
+Deletes the artifact's database row and its files. You can only delete artifacts your own token owns.
+
 ## Agent Payload Checklist
 
 Recommended fields for every agent post: