Adds docs/guides/SELF_HOST.md covering:
- Prerequisites (Node.js, pnpm)
- Build steps
- Local hosting
- LAN access (HOST=0.0.0.0, CORS, VITE_ALLOWED_HOSTS)
- Tailscale Serve — root path and sub-path (/kanban/) routing
- Reverse proxy (nginx, Caddy) with sub-path examples
- Docker / docker-compose with sub-path build args
- Security (VERITAS_ADMIN_KEY, API keys, TRUST_PROXY, roles)
- Full environment variables reference table
- Troubleshooting (CORS, WebSocket, base path, rate limits, sessions)
Original contribution by @xechehot in PR #126 — the Vite base path
and VITE_ALLOWED_HOSTS config from that PR are already merged into main;
this adds the missing documentation guide.
Co-authored-by: Brad Groux <bradgroux@users.noreply.github.com>
