feat: add git pre-push hook to prevent direct pushes to protected branches

This commit introduces a pre-push Git hook that prevents direct
pushes to the `main` and `dev` branches. This enforces the use of
pull requests for merging changes into these protected branches,
promoting code review and maintaining branch stability.

The changes include:
- Adding a `install-git-hooks` target to the Makefile to symlink
 the pre-push script into the `.git/hooks/` directory.
- Creating the `scripts/git-hooks/pre-push` script that checks the
 target branch and aborts the push if it matches a protected branch.
- Updating the `CONTRIBUTING.md` file to instruct developers to
 install the Git hooks after setting up their development
 environment.

Makefile

@@ -74,3 +74,9 @@ create-issues-from-file:
 	@echo "--> Creating GitHub issues from file..."
 	@./scripts/create_issues.py
 
+# --- Development Tools ---
+install-git-hooks:
+	@echo "--> Installing Git hooks..."
+	@ln -sf ../../scripts/git-hooks/pre-push .git/hooks/pre-push
+	@echo "✅ pre-push hook installed successfully. Direct pushes to 'main' and 'dev' are now blocked."
+