feat: apply DevsLab OSS identity to api-log

[jlc488]

Summary

• apply public oss-brand v0.1.1 O09 event-ledger identity
• add EN/KO README and source-only MkDocs assets, metadata, and Material atmosphere
• keep O09 distinct from O08/O10 and the former shared backend mark
• gate exact assets and dark contracts in CI and release

Verification

• strict MkDocs and brand checker passed
• core Gradle compilation/tests pass; local integration suite needs Docker/Testcontainers
• independent final review: spec/code/design PASS

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