docs: add the declared MIT license

[HMarzban]

The repository already declares MIT but has no standalone license file. Add the standard MIT text for Hossein Marzban and link it from the README, completing the existing licensing declaration.

Validation:

• Checked the current default branch, original licensing declaration, author metadata, repository creation year, and tracked source notices.
• Compared the license text with the existing MIT reference in express-ts-zod; only the copyright year differs.
• Confirmed the change touches only LICENSE and the README license paragraph. No source notices, dependencies, or runtime files change.
• git diff --check passed. Runtime tests were not repeated for this documentation-only change.