[codex] Add RAG pipeline guide

[Fieldnote-Echo]

Summary

• Add docs/rag-pipeline-guide.md, a developer-facing worked example for vector DB and RAG builders.
• Explain the bitmap-overlap theorem in operational terms: what it proves, what it does not prove, and how it maps to first-stage candidate admission.
• Link the guide from the README and reviewer brief, and include it in the documented-name checker.

Validation

• make check-doc-names
• make audit

[gemini-code-assist]

Code Review

This pull request introduces a new developer-facing guide (docs/rag-pipeline-guide.md) that explains how the Lean theorem translates to a retrieval system (Vector DB and RAG builders). It also updates README.md, docs/reviewer-brief.md, and scripts/check_doc_names.py to reference and track this new document. The review comments suggest minor terminology improvements in the guide to enhance clarity and statistical precision, specifically clarifying "query bits" to "active bits from the query coordinates" and "negative tails" to "null-distribution tails".

[Copilot]

Pull request overview

Adds a new developer-facing documentation page that translates the formalized bitmap-overlap theorem into vector DB/RAG operational terms, with a small worked example and a practical contract checklist. The new doc is linked from the README and the reviewer brief, and registered with the documented-name checker so its referenced Lean name stays in sync with the public surface.

Changes:

• New docs/rag-pipeline-guide.md walking through the pipeline use case, worked hypergeometric example (D=10, K=3, overlap ≥ 2), and what the theorem does and does not prove.
• README and reviewer-brief links pointing readers to the new guide.
• scripts/check_doc_names.py updated to validate Lean names referenced in the new guide.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
docs/rag-pipeline-guide.md	New developer-facing RAG/vector DB guide for the bitmap-overlap result.
README.md	Adds a link to the new guide alongside other doc pointers.
docs/reviewer-brief.md	Cross-links the new guide from the reviewer-oriented summary.
scripts/check_doc_names.py	Includes the new doc in the documented-name verification list.

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