Issue Description

scripts/dev-tools/Generate-PrReference.ps1 has the best coverage in the repo (84%) but the entry point block could use additional test cases.

Current state:

• File coverage: 84% line (93/111)
• Entry point has ~18 untested lines

Acceptance criteria:

• Add tests for edge cases in entry point parameter validation
• Test error handling paths
• Achieve ≥95% line coverage

Estimated coverage improvement: 84% → ~95%

Additional Context

Lower priority than other scripts in the test coverage initiative. Consider deferring until after higher-impact items (Get-VerifiedDownload, Package-Extension, Prepare-Extension).

This is part of a broader effort to increase unit test coverage from ~42% to ~85-90%.