fix(ci): normalize path separators in blast radius summaries

[haasonsaas]

Summary

• path.display() uses native separators, producing src\a.rs on Windows instead of src/a.rs
• The applies_blast_radius_summary_for_many_dependents test asserts on forward-slash paths, so it fails on windows-latest
• Fix: normalize backslashes to forward slashes in format_blast_radius_summary, since these paths are rendered in web UI review comments

Test plan

• CI passes on all platforms (ubuntu, macos, windows)

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Low risk: a small, presentation-only change that normalizes path formatting in generated review comments and adds a targeted unit test to prevent Windows-only failures.

Overview
Normalizes dependent file paths in blast radius review summaries by converting \\ to / when rendering PathBuf values, ensuring consistent output across platforms.

Adds a unit test (format_blast_radius_summary_normalizes_backslash_paths) to verify summaries never contain backslashes and remain stable on Windows CI.

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