feat(#208): migrate remaining mirrored tests off dist and retire dist-requiring integration tests

 Convert the last 11 mirrored private-helper tests (scaffold, quality,
 build, update) to the dot-source-first pattern so `nova test` no longer
 requires a prior `Invoke-NovaBuild`. Retire nine legacy integration and
 guardrail tests (Module, OutputFiles, BuildOptions, CiCoverage,
 CliHelperCoverage, CliSharedParser, PackageLatestPolicy, PreambleBuild,
 UpdateNotification) and their TestSupport sidecars to `tests/_legacy/`
 with the `.LegacyReference.ps1` suffix so Pester discovery skips them.
 Their behavior is now covered by the mirrored source-file tests added
 in #200 – #207.
 closes Pester redesign for NovaModuleTools
 Fixes #208

Author: stiwicourage