docs(agents): align triage state labels

[elezar]

Summary

Align the triage skill with the repository’s state-label workflow and clarify who may change each label.

Related Issue

No issue required: localized agent-workflow documentation correction.

Changes

• Document the triage, disposition, delegation, and execution state labels.
• Keep state:accepted and state:agent-ready human-only.
• Permit triage agents to apply evidence and routing labels only.

Testing

• mise run markdown:lint passes in ~/.dotfiles/devenvs/openshell.
• mise run pre-commit passes (blocked because cargo is unavailable in that devenv session).
• Unit tests added/updated (documentation-only change).
• E2E tests added/updated (not applicable).

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)