[Beginner]: Add an `.editorconfig` file to standardize code formatting

Description

Create an .editorconfig at the root of the repository to enforce 4 spaces for Python, 2 spaces for JSON/YAML, UTF-8 charset, and final newlines.

Why it matters

Ensures that all contributors automatically use the correct tab/space settings in their IDEs before they even hit pre-commit hooks.

Acceptance Criteria

• [ ] Create .editorconfig
• [ ] Define rules for *.py, *.yml, *.md
• [ ] Ensure it enforces trim-trailing-whitespace and final newlines
• [ ] Passes pre-commit run --all-files