Fix consistent-data-testid fileName on Windows paths

[sjh9714]

Summary

Fixes {fileName} replacement in consistent-data-testid when ESLint reports Windows-style paths.

What changed

• Added regression coverage for a Windows path in the filename test case.
• Updated filename extraction to handle both POSIX and Windows path separators.
• Preserved the existing index file and dynamic route filename behavior.

Why

Issue #782 reports that {fileName} can expand to the full Windows path instead of just the component file name because the rule only splits paths on /.

Testing

• pnpm test tests/rules/consistent-data-testid.test.ts
• pnpm run lint
• pnpm run type-check
• pnpm test
• git diff upstream/main...HEAD --check

Fixes #782