docs: comprehensive multi-tool integration documentation (#328)
- New docs/integrations.md (607 lines) — full per-tool guide for Cursor, Aider, Kilo Code, Windsurf, OpenCode, Augment, Antigravity
- Updated getting-started.md with install tabs for all 7 new tools
- Updated index.md — 11 platforms listed, multi-tool button added
- Updated mkdocs.yml nav + site description
- Updated README.md — 11 tools, expanded FAQ
Each tool section includes: format spec, install (script + manual), verify, customization tips, and troubleshooting.
Co-authored-by: Leo <leo@openclaw.ai>