Adds docs/guides/deployment.md covering Docker Compose quick-start and
bare-metal step-by-step deployment: prerequisites, DB init, build, systemd
service units, nginx/Caddy reverse proxy config, security checklist, and
troubleshooting section.
Expands .env.example with all environment variables found in the codebase,
including NEXT_PUBLIC_GATEWAY_URL, agent sandbox/tool/system-prompt settings,
embedding and summarization API config, MCP_SERVERS, MOSAIC_WORKSPACE_ROOT,
OLLAMA_MODELS, and MOSAIC_CUSTOM_PROVIDERS, with defaults and descriptions.
Closes#58
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
