feat: add GitHub issue triage workflows

[ThomasK33]

Summary

• Add reusable project GitHub workflow actions for issue listing, conversation retrieval, automation-state checks, comment verification, label mutation, and project context resolution.
• Add a durable github-issue-triage workflow that reconciles GitHub issues into persistent triage workspaces, uses triage:ongoing/triage:done labels for state, and verifies published triage comments before marking issues done.
• Add a simplify workflow that delegates reuse, quality, and efficiency review lanes, synthesizes findings, and can safely apply fixer patches after git preflight.

Behavior changes

• /workflow github-issue-triage can discover untriaged issues, create or reuse per-issue workspaces, send maintainer-facing triage prompts, publish verified comments, and update triage labels idempotently.
• /workflow simplify is available as a reusable review/fix workflow for current git changes or explicit refs.
• New workflow actions are discoverable through the workflow action registry and use strict input/output schemas.

Validation

• npm run format:check
• node --check for all changed .mux/**/*.js and .mux/**/*.cjs files
• workflow_action_list
• workflow_list

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Generated with mux • Model: openai:gpt-5.5 • Thinking: xhigh