fix(coverage): probe the pwsh exemption with the executor's own resolution

The review caught the pwshCoverageExclusions comment claiming the inverse of
the code's behavior: a bare-PATH probe FAILING grants the exemption, so a
win32 host where only install-location pwsh (or 5.1) resolves kept the
exemption while its suites ran - over-exempting, never tightening.

resolvePwshPath/candidatePwshPaths move to the dependency-free
pwsh-local/src/resolve.ts (index.ts re-exports; public API unchanged) and
vitest.config.ts probes with that shared definition, so the exemption is
active exactly when the suites skip. The two spec headers stop saying
'on PATH' for a probe that is deliberately not PATH-only, and the parity
note records the abort backport as the one both-ways parity change (both
languages, pairing re-recorded); catalogs regenerated for the line shift.

packages/bash/pwsh-local/tests/executor.spec.ts

@@ -3,8 +3,8 @@
  * service plus a REAL pwsh executable, exercised through the executor seam
  * (`resolve` → `run`/`start`). These verify the world — actual PowerShell
  * runs, output capture, truncation and spill, deadlines, kill escalation, and
- * the background-handle contract. The suite self-skips when no `pwsh` is on
- * PATH (a CI accommodation for hosts without PowerShell); the pure unit tests
+ * the background-handle contract. The suite self-skips when no usable `pwsh`
+ * resolves (a CI accommodation for hosts without PowerShell); the pure unit tests
  * (config validation, executable resolution) run on every platform. PowerShell
  * writes CRLF on Windows, so exact text assertions normalize line endings.
  */