Add template selection to CLI

[Ochibueze474]

This PR implements template selection as requested in issue #2.

• Added display_templates() in templates.py to show a numbered list
• Added select_template() to accept user input, validate it's a real number and within range, and return the chosen template name
• Wired it into main.py so the tool now shows templates and prompts for a selection on run
• Tested locally with valid input, out-of-range numbers, and non-numeric input, all handled correctly

I kept this scoped to selection and validation only, not connecting it to the generator yet, since generating the right files per template looks like it's covered separately in issue #3.
Let me know if you'd prefer it wired together here instead.

Fixes #2