Add root-level .gitattributes for cross-platform consistency

### Describe the solution you'd like

The repository currently does not define a root-level `.gitattributes` file for line ending normalization and cross-platform Git consistency.

Adding a `.gitattributes` configuration would help standardize:
- line endings
- text normalization
- binary file handling
- cross-platform contributor workflows

This would reduce formatting inconsistencies between Windows, Linux, and macOS environments.

### Describe alternatives you've considered.

Contributors can currently rely on local Git configuration manually, but repository-level normalization would provide more predictable behavior across environments.