Add .gitattributes to enforce LF line endings

[xterao]

This pull request unifies newline settings across Spotless, Git configuration, and IntelliJ to ensure consistency. By standardizing newline characters, only intentional code changes are shown without spurious newline-only diffs.

Changes include:

• Configuring Spotless to enforce a consistent newline code (LF).
• Updating Git settings to standardize commit newline codes.
• Adjusting IntelliJ settings to align with the project-wide LF standard.

These changes improve code readability and reduce unnecessary diff noise.