Answer whoami --role from the repository's rules

Why

A role is per repository, so vole whoami cannot print one role without first knowing which repository is meant. The default answer stays the account name because scripts such as -a "$(./vole whoami)" depend on it; the role is an explicit question.

What changed

vole whoami --role prints the effective role the key holds on the repository named by the remote:

vole whoami          # keenan
vole whoami --role   # admin

• The client sends the current remote’s repository path to the server’s vole-whoami verb.
• The server resolves the repository’s ACL: its default and per-account rules, with the instance-wide role applied where the repository is public.
• A private repository the account cannot read is reported as not found, the same as a fetch, rather than revealing the repository or a role.
• A run credential may ask only about its own repository.
• The default vole whoami response is unchanged.

The CLI help, AGENTS.md, CONTRIBUTING.md, and the account, CLI and getting-started docs point at the new query.

Verification

• go test -tags sqlite_fts5 ./...
• New TestWhoAmIRoleAnswersFromTheInstance covers the repository owner, a maintainer, a private repository hidden from a stranger, and the public default role.
• python3 scripts/check-links.py
• ./vole workflow check