fix: add modal type to subscriptionEligibility

[tuna1207]

Explanation

Add missing modalType field and constant to SubscriptionEligibility

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

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Note

Adds optional modalType to SubscriptionEligibility, introduces MODAL_TYPE/ModalType, and updates exports and tests.

• Types:
  • Add MODAL_TYPE constant and ModalType type in src/types.ts.
  • Extend SubscriptionEligibility with optional modalType field.
• Exports:
  • Export ModalType and MODAL_TYPE from src/index.ts.
• Tests:
  • Update SubscriptionController.test.ts to import MODAL_TYPE and include modalType in eligibility mocks.
• Changelog:
  • Document addition of modalType field and constant in CHANGELOG.md.

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