feat(create-gen-app): make MIT the default license

[pyramation]

Summary

Makes MIT the default license option in create-gen-app by:

1. Adding a DEFAULT_LICENSE = 'MIT' constant
2. Adding a CLOSED_LICENSE = 'CLOSED' constant
3. Modifying listSupportedLicenses() to return licenses in a specific order:
   • MIT first (as the default)
   • Other licenses alphabetically in the middle
   • CLOSED last

When boilerplate templates use "optionsFrom": "licenses", MIT will now appear as the first option and CLOSED will appear last.

Review & Testing Checklist for Human

• Verify that having MIT first in the options list actually makes it the default selection in the prompts (test by running a scaffolding command that uses the license question)
• Verify CLOSED appears last in the license list when prompted
• Confirm the DEFAULT_LICENSE and CLOSED_LICENSE exports are useful for any downstream code that might need to reference these values

Notes

• All existing tests pass (28 tests)
• The sort order is: MIT → alphabetical (APACHE-2.0, BSD-3-CLAUSE, GPL-3.0, ISC, MPL-2.0, UNLICENSE) → CLOSED

Link to Devin run: https://app.devin.ai/sessions/a51e296fcb614c0294cf1678407a08f3
Requested by: Dan Lynch (pyramation@gmail.com) / @pyramation

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