fix(runtime): normalize Windows workspace paths

[SulimanAbdulrazzaq]

Summary

• Normalize Windows extended-length (\\?\) and regular path representations before enforcing workspace boundaries.
• Cover DOS and UNC prefix variants with regression tests.

Fixes #3278

Anti-slop triage

• Classification: actionable-fix
• Evidence: Reproduction and Windows path-prefix analysis in grep_search: spurious "escapes workspace boundary" on first run in a directory with no .claw/ (Windows) #3278; no matching active PR found.
• Non-destructive review result: merge candidate

Verification

• cargo fmt --manifest-path rust/Cargo.toml --all -- --check
• git diff --check
• cargo +stable-x86_64-pc-windows-gnu check --manifest-path rust/Cargo.toml --target x86_64-pc-windows-gnu -p runtime
• cargo +stable-x86_64-pc-windows-gnu clippy --manifest-path rust/Cargo.toml --target x86_64-pc-windows-gnu -p runtime --lib (completed with existing warnings outside this change)
• Runtime unit tests: the repository's Windows-target test build currently fails in pre-existing Unix-only std::os::unix::fs::PermissionsExt tests; the default MSVC toolchain also lacks link.exe in this environment.
• No secrets, tokens, private logs, or unrelated generated files are included.

Resolution gate

• This PR resolves grep_search: spurious "escapes workspace boundary" on first run in a directory with no .claw/ (Windows) #3278 with a focused path-comparison fix and regression coverage.