Add v0.3 Bash and PowerShell design corpus

[Aaronontheweb]

Summary

• add 17 Bash and 17 PowerShell pre-implementation contract cases
• record current v0.2 behavior beside desired syntax, command occurrences, bounded values, redirects, compatibility, and security invariants
• validate schema shape, references, deterministic command order, live v0.2 expectations, fixed 32-candidate boundaries, and PII safety
• lock the v0.3 public record hierarchy and safe defaults, immediate role plus compositional ancestry, fixed 32/16/5 limits, shared Clause identity, pattern/cwd rules, unparseable projection behavior, and separate Bash/PowerShell grammar matrices
• add an explicitly unshipped v0.3 migration contract to the consumer guide and update project context

Contract outcomes

• structurally complete occurrences may still contain unknown values
• PowerShell authored parameter classification remains distinct from effective values; native values are reinterpreted by executable grammar
• unparseable results expose empty Commands and Clauses; partial Syntax is diagnostic only
• heredoc body interpretation, process substitution, background lists, case/switch, arithmetic/C-style loops, and definitions stay deferred beyond stable v0.3
• SPEC.md and SPEC.POWERSHELL.md synchronization remains paired with the production API and snapshot-test change so repository authority never drifts from the assembly

Validation

• dotnet tool restore
• dotnet build -c Release
• dotnet test -c Release --no-build (1,019 passed)
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify
• openspec validate v0-3-structured-shell-analysis --strict
• isolated compilation of the locked public record hierarchy
• parse-only oracle checks using bash -n and the PowerShell language parser

Tracks #72 and supplies contract cases for #71.