docs: external orchestration frameworks, pr-triage skill, GitHub Actions templates

Added:
- guide/third-party-tools.md: External Orchestration Frameworks section
  (Ruflo + Athena Flow) with architectural distinction from multi-instance tools
- examples/skills/pr-triage/: 3-phase PR backlog management skill
  (audit, deep review via parallel agents, validated comment posting)
- examples/github-actions/: claude-code-review.yml + .coderabbit.yaml +
  prompts/code-review.md — AI-powered PR review GitHub Actions workflow
- docs/resource-evaluations/073-athena-flow-workflow-runtime.md (2/5 Watch)
- docs/resource-evaluations/074-ruflo-multi-agent-orchestration.md (3/5 Pertinent)

Updated:
- examples/README.md + examples/github-actions/README.md: new templates indexed
- machine-readable/reference.yaml: new entries for github-actions + pr-triage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

machine-readable/reference.yaml

@@ -877,6 +877,12 @@ deep_dive:
   ai_ecosystem_voice_to_text: "guide/ai-ecosystem.md:1066"
   ai_ecosystem_alternative_providers: "guide/ai-ecosystem.md:2639"
   voice_refine_skill: "examples/skills/voice-refine/SKILL.md"
+  # PR Triage Skill (added 2026-03-05)
+  pr_triage_skill: "examples/skills/pr-triage/SKILL.md"
+  pr_triage_template: "examples/skills/pr-triage/templates/review-comment.md"
+  pr_triage_phases: "3 (audit + deep review + validated comments)"
+  pr_triage_when: "5+ open PRs, periodic backlog triage, post-sprint cleanup"
+  pr_triage_vs_review_pr: "pr-triage = backlog N PRs | review-pr = single PR focus"
   # Cowork documentation (v1.0 - migrated to dedicated repo)
   cowork_reference: "machine-readable/cowork-reference.yaml"  # Dedicated YAML index (kept local)
   cowork_hub: "https://github.com/FlorianBruniaux/claude-cowork-guide/blob/main/README.md"