Add rag engineer

[ai-turn]

What does this PR do?

Adds a new Engineering agent: RAG Engineer.

This agent specializes in production RAG design, debugging, and improvement. It focuses on diagnosing poor answers through the evidence chain first: corpus, chunking, embeddings, retrieval, reranking, prompt grounding, observability, and evals. The core idea is to avoid blaming the LLM model before verifying whether the right evidence was retrieved and presented to the generator.

Agent Information (if adding/modifying an agent)

• Agent Name: RAG Engineer
• Category: Engineering
• Specialty: Production RAG systems, retrieval debugging, grounded generation, citation behavior, and evaluation loops

Checklist

• Follows the agent template structure from CONTRIBUTING.md
• Includes YAML frontmatter with name, description, color
• Has concrete code/template examples (for new agents)
• Tested in real scenarios
• Proofread and formatted correctly

[msitarzewski]

Thanks for this, @ai-turn — solid RAG agent. We had a concurrent submission (#601, RAG Pipeline Engineer) covering the same specialty, and after a detailed comparison we merged that one as the keeper (it was submitted first and is ~2× the content). So I'm closing this as a duplicate — no reflection on the quality.

One genuinely great thing yours has that #601 doesn't: the explicit Symptom → Evidence Chain → Root Cause → Smallest Fix debugging framework. That's sharper than anything in the merged agent. If you're up for it, we'd love a follow-up PR that grafts that framework into engineering/engineering-rag-pipeline-engineer.md — it'd genuinely improve it, and you'd get the credit. 🙏