test(atomic-a11y): add unit tests for OpenACR converter modules

[y-lakhdar]

TL;DR

Unit tests for the OpenACR converter modules added in PR #7124.

Extracted into a separate PR to keep #7124 focused on the implementation (~1,100 LOC) and this PR focused on test coverage (~1,500 LOC).

Test coverage

Test file	Tests	Module under test
conformance.test.ts	23	mapCriterionConformance, resolveConformance priority chain, buildRemarks for all conformance states
json-to-openacr.test.ts	5	End-to-end conversion, missing input fallback, override application, YAML output
manual-audit.test.ts	26	Baseline validation, parsing, status filtering, conformance mapping, directory loading, resolveManualConformance precedence
overrides.test.ts	7	Loading, validation, all conformance values, error handling
openacr-report-builder.test.ts	12	Full report build, null input, overrides, manual data, chapters, summary

Total: 73 tests

Try it

cd packages/atomic-a11y
pnpm build && pnpm test

PR Chain (6 of 8)

#	PR	Description
1	#7111	Package scaffolding
2	#7122	Shared types, constants, utilities
3	#7123	VitestA11yReporter + wiring
4	#7137	Shard merging for parallel CI runs
5	#7124	OpenACR report generator
6	this PR	OpenACR converter tests
7	#7125	CLI scripts
8	#7117	Weekly a11y scan workflow

KIT-5470