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>

examples/github-actions/prompts/code-review.md

@@ -39,6 +39,22 @@ For any file that looks non-trivial, use `Read` to see the full implementation c
 
 ---
 
+## Step 1b — Load Stack-Specific Skills (Optional)
+
+If your project has skill guides in `.claude/skills/`, load the relevant ones based on what the diff touches. Run `Read` on matching paths if they exist:
+
+| If the diff contains... | Load this guide |
+|------------------------|-----------------|
+| `auth`, `session`, `token`, `password` | `.claude/skills/security-guardian/authentication/` |
+| `sql`, `query`, `prisma`, `db` | `.claude/skills/postgres-*/SKILL.md` or your DB guide |
+| `input`, `form`, `upload`, `file` | `.claude/skills/security-guardian/input-validation/` |
+| `api`, `endpoint`, `route`, `middleware` | Your API conventions doc |
+| `payment`, `stripe`, `billing` | Your payment integration guide |
+
+Skip this step entirely if no matching skills exist or the diff is small.
+
+---
+
 ## Step 2 — Analyze Changes
 
 Review each changed file through these lenses: