GitLab

- Add formatCompactNumber() for consistent large-number formatting (K/M/B)
- Include last_used_at in OpenAI usage refresh key for better change detection
- Add .gitattributes eol=lf rules for frontend source files

Ensures consistent line endings for SQL migration files, Go source,
shell scripts, YAML configs, and Dockerfiles. Fixes checksum mismatches
on Windows where CRLF line endings cause migration hash differences.