docs(standards): align Git Tags section with PR-based release workflow

[rocketman-code]

The Git Tags section in docs/standards/releases.md (line 52) says:

Tag the version bump commit.

But the updated release checklist step 10 now says:

After merge, tag the merge commit

With branch protection, these are different commits. The Git Tags section should be updated to say "Tag the merge commit on main" (or similar) for consistency.

Similarly, line 58 says "Update the changelog as part of the release commit, before tagging" which doesn't reflect the PR-based workflow where the changelog is a separate commit in the release PR.

Found during code review of PR #202.