Add explicit type annotation to CONSTANT export

[Lang-Qiu]

Problem

The exported constant CONSTANT in src/constants/index.ts lacked an explicit type annotation. This could lead to ambiguous types in TypeScript, making the code harder to understand and maintain, potentially causing issues with type inference and readability.

Changes

• Introduced a Constants interface to define the shape of the CONSTANT object, specifying the types for I18N, CHECKSUMS, and PUBLIC_ROUTES based on their respective imports.
• Added an explicit type annotation to the CONSTANT variable using the new interface, ensuring type safety and clarity.

Verification

• Confirm TypeScript compilation completes without errors (e.g., run tsc or similar build process).
• Run existing tests (if available) to ensure no functionality changes or regressions.
• Review the diff to verify the changes align with the intended improvement in type annotations.