Agent Skills: git-identity

Multi-identity Git configuration with directory-scoped isolation. Sets up per-directory user email, GPG signing keys, and SSH keys using includeIf conditional includes. Use when configuring work vs personal Git identities, fixing "Unverified" commits from email/GPG key mismatch, setting up multiple GitHub accounts on one machine, auditing identity isolation, or troubleshooting includeIf, GPG key selection, or SSH key routing issues.