Add loading animation while DevHands is generating files

Description: When a user selects "Create new app", DevHands currently prints a message and generates the folder structure. Improve the user experience by adding a simple "loading" animation during the process.

Tasks:

• Add a helper function (e.g. show_spinner()) that displays a rotating character or progress dots while files are being created.
• Use threading or a simple loop with time.sleep().
• Print a clean "✅ Done!" message once generation is complete.
• Ensure this works in both Docker and native terminal environments.