test(config-audit): add baseline-all-a fixture + grade-stability regression test

plugins/config-audit/tests/fixtures/baseline-all-a/CLAUDE.md

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+# Baseline Project
+
+## Overview
+
+A fixture designed to score Grade A on every v3 quality area (CML, SET, HKV,
+RUL, MCP, IMP, CNF) before the Token Efficiency scanner is added. Serves as
+the grade-stability canary for the config-audit v4.0 release.
+
+## Purpose
+
+This fixture is the regression canary for the posture scorecard. If a future
+scanner change drags any v3 quality area below Grade A on this fixture, the
+change is not release-safe.
+
+## Commands
+
+- `npm run build` — Build the project
+- `npm test` — Run all tests
+- `npm run lint` — Lint source files
+
+## Architecture
+
+Standard Node.js layout with TypeScript under `src/`, unit tests co-located
+beside implementation files, and shared config imported via `@import`.
+
+## Conventions
+
+- TypeScript strict mode; no `any`
+- Conventional Commits (`type(scope): description`)
+- Zero runtime npm dependencies where possible
+- Deterministic test fixtures only
+
+## Tooling
+
+- Node.js ≥ 18
+- `node:test` framework for unit tests
+- `node --test 'tests/**/*.test.mjs'` runs the full suite
+
+## Shared Patterns
+
+Shared conventions and helpers are documented in an imported file to keep the
+top-level stable-prefix content cache-friendly under Opus 4.7.
+
+@.claude/shared.md