feat: apply DevsLab OSS identity to ssrf-guard

[jlc488]

Summary

• apply public oss-brand v0.1.1 O02 protected-boundary identity
• add EN/KO README and source-only MkDocs logo, favicon, social metadata, and portable Material atmosphere
• preserve all 12 published modules and shared O02/O03 security geometry
• validate exact assets, metadata, module compatibility, and Material slate dark cap

Verification

• Gradle build + Jacoco passed
• brand checker passed
• independent final review: spec/code/design PASS
• strict MkDocs is blocked only by two pre-existing missing KO links outside this diff

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