v1.3.23 — test environment diagnostics

I added bounded test-environment diagnostics to the existing source and extracted-release test entry points. npm test now observes directory-link fixture setup before starting the unchanged suite. A denied or unknown preflight reports validation as incomplete; --run-tests explicitly runs the full suite when useful and preserves original TAP, errors, counts and exit status.

Actual link-setup failures retain their original errors and add a scoped diagnostic. Cleanup failures remain visible. Probe success does not guarantee later fixture success, and EPERM does not by itself establish an administrator requirement or explain unrelated assertions. No safety assertion or required gate is skipped or weakened.

Nine diagnostics regressions cover controlled supported, denied, unexpected and mixed failures, missing execution, cleanup/reporting failures and default Node discovery. Existing CI jobs and protections are retained, with no new dependency, service, retry engine, timeout increase or automatic remote dispatch. The installed skill payload is unchanged; this release updates repository testing tools and contributor guidance.

Windows source and extracted-package tests passed 482/482 with no skips. Review and final validation: PR #53. Review was same-agent, source-exposed. Local junction preflights remained incomplete; CI passes do not relabel those denials.

Exact Windows-verified ZIP SHA-256: fc8ba18685df08ded3153977015778600c0cc2327f1bea44c3cd721b576b7207 (2,194,126 bytes).