Add app name validation

[Aditya-vegi]

Description

Adds validation to app name input to prevent invalid names from breaking folder creation and app configuration.

Problem

Users could enter invalid app names containing spaces or special characters, which would cause issues with:

• Folder creation
• Slug generation
• App compatibility

Solution

Added input validation that only allows:

• Letters (a-z, A-Z)
• Numbers (0-9)
• Hyphens (-)

Invalid names show a clear error message.

Changes

• Added regex validation: /^[a-z0-9-]+$/i
• Validates app name immediately after user input
• Shows helpful error message for invalid input

Type of Change

• Bug fix (prevents invalid app names)
• New feature (validation logic)

Testing

npm run build
rc-apps create

# Test cases:
# 1. Enter "My App" → Should show error
# 2. Enter "@invalid" → Should show error
# 3. Enter "my-app" → Should continue