feat: add pre-commit hook setup script

- Add `scripts/setup-pre-commit.sh` to install a git pre-commit hook.
- The hook runs `npm run lint` and `npm run build:css` to enforce quality and build consistency.
- Update `CONTRIBUTING.md` to document the new hook setup under Development Setup.

CONTRIBUTING.md

@@ -74,6 +74,12 @@ To set up the project locally:
    npm run lint
    ```
 
+5. **Git Hooks (Optional)**:
+   We provide a script to set up a git pre-commit hook that runs linting and CSS builds automatically before you commit.
+   ```bash
+   ./scripts/setup-pre-commit.sh
+   ```
+
 For a full guide, see the [Local Setup section in README.md](./README.md#local-setup).
 
 ## Dev Container