feat: apply DevsLab OSS identity to devslab-kit - #71

Summary

• apply public oss-brand v0.1.1 O10 toolkit identity
• add EN/KO README and source-only MkDocs logo, favicon, social metadata, and Material atmosphere
• preserve canonical dirty .claude and generated site trees
• gate exact assets and dark-mode contracts in routine build and release workflows

Verification

• Gradle build + coverage passed (80 tasks)
• strict MkDocs and brand checker passed
• independent final review: spec/code/design PASS

Canonical guide: https://devslab.kr/brand/open-source/