Add AI readiness engineering best-practices audit

[oly-agents]

Summary

AI readiness audit of patterninc/blurb per the gauge-repo skill (rubric item-credit-v1, 2026-09-04), requested by ClickUp task 86e372wd5 (AI Readiness Audit — Batch 2/9, Infra Cost Center).

Adds docs/engineering-best-practices-audit.md:

• Critical gates: RED — AGENTS.md and required CI checks are Gaps; unit tests, integration tests, and reproducible builds are Partial.
• Adjusted compliance: 30.3% (8 Met + 0.5 × 4 Partial over 33 applicable items; 16 profile-backed N/A for this deploy-less Ruby gem).
• Top recommendations: make CI actually run the spec suite and require it before merge; add AGENTS.md; stub the live-Amazon-API specs with WebMock/VCR so they run hermetically.

Documentation-only change; no code touched.

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Oly run: https://oly.pattern.com/runs/01a08bfa-1e1a-747e-92f7-a3ce048c5ddc
Requested by: abhinav.nsingh@pattern.com

[vivekb-pattern]

Approved — docs-only change adding the gauge-repo AI-readiness / engineering best-practices audit. Verified: single new file under docs/, no source, workflow, IaC, or config changes; all checks passing.