test(directory-layout): move sanitizer tests next to src/readme-html-sanitizer.ts

[kitsuyui]

Why

scripts/ is this repo's home for operational/support scripts, but its only unit test file, scripts/check-readme-sync.test.ts, also directly exercised src/readme-html-sanitizer.ts (the runtime module that sanitizes the rendered README HTML), not just the readme-sync script it is named after. package.json's test:unit was pinned to that single file, so the sanitizer's tests had no tree-visible location of their own. A contributor changing src/readme-html-sanitizer.ts could not infer from the directory layout where its test lived, widening the search on every sanitizer change.

What changed

• Moved the sanitizer test cases out of scripts/check-readme-sync.test.ts into a new src/readme-html-sanitizer.test.ts, co-located with the module they test.
• The new file imports sanitizeReadmeHtmlTree from ./readme-html-sanitizer and the upstream repo constants directly from ./upstream-readme-source, instead of going through the scripts/check-readme-sync.ts re-export.
• scripts/check-readme-sync.test.ts now only covers checkReadmeSync (the readme-sync script itself).
• Updated test:unit in package.json to run both test files explicitly.

No behavior changes: the same 17 test cases still run, unchanged.

Verification

• bun test scripts/check-readme-sync.test.ts src/readme-html-sanitizer.test.ts -- 17 pass, 0 fail.
• biome check . -- passes (only a pre-existing, unrelated config deprecation notice).

Finding: audit-directory-layout-audit-003.

[github-actions]

Code Metrics Report

	main (6219157)	#983 (5cb1eed)	+/-
Coverage	91.2%	91.2%	0.0%
Code to Test Ratio	1:0.9	1:0.3	-0.6
Test Execution Time	13s	18s	+5s

Details

  |                     | main (6219157) | #983 (5cb1eed) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          91.2% |          91.2% | 0.0% |
  |   Files             |              3 |              3 |    0 |
  |   Lines             |            114 |            114 |    0 |
  |   Covered           |            104 |            104 |    0 |
- | Code to Test Ratio  |          1:0.9 |          1:0.3 | -0.6 |
  |   Code              |            306 |            793 | +487 |
  |   Test              |            288 |            288 |    0 |
- | Test Execution Time |            13s |            18s |  +5s |

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Reported by octocov