[OpenClaw] chore: add .gitignore for static site

[Kumazan]

TL;DR

Add .gitignore to prevent OS metadata (.DS_Store), editor files, and future tooling artifacts from showing in git status.

SDD Summary

• Goal: Prevent untracked artifacts from polluting git status
• Scope: 1 file added (.gitignore) — no content changes
• Approach: macOS + editor + light Node/Python patterns

Test Results

Command	Result
git check-ignore .DS_Store	✅ matched
git status	✅ only .gitignore + SDD.md as new files

Risks & Rollback

• Risk: None — only affects untracked files
• Rollback: Delete .gitignore

TODO

• None

size:small · date:20260315

[Kumazan]

@github-copilot please review