feat(setup): add robust input validation for user prompts

[talaatmagdyx]

Description:

This PR enhances the gitmeright setup script by introducing input validation to ensure that all required user inputs (GitHub username, full names, emails, and project names) are not left empty.

🔧 Changes Introduced:

• Added a reusable prompt_and_validate Bash function that:

  • Prompts the user for input.
  • Loops until a non-empty response is provided.

• Replaced all read -p prompts with the new validation wrapper to enforce required input.

• Improved the user experience by displaying clear error messages for missing input.

✅ Benefits:

• Prevents misconfigured .gitconfig files due to empty placeholders.
• Reduces setup errors and manual cleanup.
• Ensures consistent SSH key generation and Git identity setup.

🧪 Testing:

• Ran the script locally with valid and invalid inputs to confirm validation works as expected.
• Verified that .gitconfig files are correctly populated and no silent failures occur.

[s403o]

@talaatmagdyx Thanks for the contribution! I've tested the changes, and everything works as expected. Looks good to me!