docs(triage): adopt GitHub-only triage duty skills #4506

User Story

As an OpenShell maintainer adopting the triage-duty tooling in #3082, I need a GitHub-only queue review and a safe way to apply one selected recommendation, so that incoming work remains visible and duty handoffs preserve public waiting context.

Description

Adopt Evan Lezar's triage-duty skills with his permission and address the review feedback on #3082. Queue review stays read-only; application selects a stable source-object ID and previews and confirms each external write.

Context

Source PR: #3082

The review requests current-main compatibility, correct intake-gap eligibility, stable IDs across reports, independent new/carried recommendation budgets, a historical backlog cursor, and durable shareable deferrals. Follow-up feedback requests removal of Slack tooling and the obsolete architecture plan.

Definition of Done

• Both contributor skills are registered and marked internal on current main.
• Slack tooling, internal identifiers, obsolete plan, and unnecessary UI metadata are absent.
• Intake-gap routing excludes all lifecycle state labels and intentionally routed issues.
• Stable source IDs cannot resolve to a different item in a later report.
• Carried items cannot crowd new intake out of the decision budget; historical discovery advances independently.
• Local files are ignored, reports are immutable snapshots, and action records define disposition authority.
• Shareable waiting context can be published through a separate per-write approval gate; closure is a distinct action.
• A report template and scoped formatting, link, and discovery checks cover the skills.