Add explicit PowerShell redirect analysis

[Aaronontheweb]

Summary

• add occurrence-level PowerShell redirect facts without changing the v0.2 compatibility projection
• match native PowerShell redirect grammar, including duplicate-source rejection, descriptor merges, and null sinks
• resolve bounded redirect targets through foreach state, cwd joins, and nested wrapper invocation ownership
• expand the generated PowerShell corpus to 417 cases and update OpenSpec, the consumer guide, and implementation plan

Validation

• Release build: clean, zero warnings
• Tests: 2,370 passed
• PowerShell corpus: 417 entries regenerate exactly
• Public API snapshots: 37 passed
• OpenSpec strict validation: passed
• Header verification: passed
• Slopwatch: zero findings
• Adversarial review: GO on immutable staged hash c37d6530990fdf36516156f343aa57e4e744c4b1e0e9b009309bff9b4896e5ec