Correct PowerShell authored command completeness

[Aaronontheweb]

Summary

• define PowerShell completeness at the submitted authored-command boundary
• keep ambient profiles, modules, aliases, functions, PATH, variables, and prior runspace state outside that proof
• retain parser-owned native versus script binding for explicit path-shaped commands
• keep unqualified script names, dynamic execution, explicit mutations, and policy-sensitive provider loops strict
• regenerate the 491-case PowerShell corpus and align OpenSpec and implementation guidance

Verification

• dotnet build -c Release: 0 warnings, 0 errors
• dotnet test -c Release: 2768 passed
• focused PowerShell tests: 977 passed
• PII audit: passed
• header verification: passed
• openspec validate v0-3-structured-shell-analysis --strict: passed
• Slopwatch: 0 issues
• adversarial review: PASS, no blocking findings