feat: add deep gitlawb parity — secrets, trust VCs, maintainers, DID methods, repo tokenize

New commands:
- gt identity resolve/register-did — did:gitlawb and did:web methods
- gt cert threshold/sign — signed ref-update certificates
- gt secrets list/set/get/delete — KMS-backed secret management
- gt trust show/issue/verify — Verifiable Credential trust scores
- gt maintainers list/add/remove — .gitant/maintainers file
- gt repo tokenize — deploy ERC-20 token per repo

Author: Patel230