guardrails: reference-verify skips recorded eval samples (evals/**/samples/) #10694

Slice of #9936.

Problem

The guardrails pre-push reference-verify entry blocked the push of #9936's eval scenario sources with 28 findings, every one dotnet build --nologo (not in 'dotnet build --help'), and every one in a labeled judge sample under plugins/developer-experience/evals/sources/labels/*/samples/. Those files are recorded model output. A flag, skill reference or path inside them is data, not a claim the repository makes (docs/conventions/untrusted-content/README.md), and eval cases keep recorded output as recorded (.claude/rules/eval-case-transcripts.md). Editing them to pass the check would corrupt the eval, so the check is a false positive on these files.

This is a hook-precision fix (docs/conventions/hook-precision/README.md): it narrows which files a verifier reads. It does not change what the verifiers enforce on authored text, and it is not a security-control change.

Rule

• Skip only files in a samples/ folder below an evals/ folder (at the repository root or nested, directly or deeper), in the one filter that picks which changed files go to the three verifiers (cli-flag-verify, skill-reference-verify, stale-path-verify).
• Prompts, graders, fixtures and harness files of an eval suite stay verified.
• A samples/ folder outside evals/ stays verified.

Done when

• A stay-quiet test that fails before the fix: an unknown flag in plugins/p/evals/c/samples/answer.md and in evals/sources/labels/T1/samples/run1.md does not block the push.
• Must-fire tests pass before and after the fix: the same unknown flag still blocks in plugins/p/evals/c/graders/check.md, plugins/p/evals/c/prompt.md and docs/samples/x.md.
• plugins/guardrails/git-hooks/reference-verify.test.sh passes in full.
• The guardrails README entry row says which files the entry skips.
• Pushing chore(developer-experience): commit the hand-rolled eval scenario sources #9936's eval-sources branch through the hook reports no findings in the samples/ files.