chore: audit repository-standards.md for correctness

[wphillipmoore]

Problem

The repository-standards.md may contain stale information that drifted as
the tooling evolved. Known patterns of drift include incorrect flag references,
outdated tool names, and inaccurate CI gate descriptions.

Checks to perform

• vrg-commit flags (--type, --scope, --message, --body are the actual flags)
• vrg-submit-pr flags and defaults (--linkage default is now Ref, not Fixes)
• CI gate descriptions (check names may have changed with vergil-actions migration)
• Tool name references (st-* vs vrg-* naming)
• Any other references to CLI tools, workflows, or conventions that may have changed

Location

docs/repository-standards.md

Context

Tracks vergil-project/vergil-tooling#1013

[wphillipmoore]

Fixed in #506