fix(api): remove duplicate CredentialNFT import and unused CredentialMetadata (#520)

[lmduy2612]

Summary

Closes #520.

Removes duplicate CredentialNFT type import and unused CredentialMetadata type import from src/lib/api/credentials.ts, while organizing top-level imports cleanly.

Changes Made

• Consolidated import statements at the top of src/lib/api/credentials.ts.
• Removed line 24 duplicate CredentialNFT and unused CredentialMetadata.
• Verified that all unit tests in src/lib/api/credentials.test.ts pass 100% and ESLint reports zero errors.

Acceptance Criteria

• Remove line 3 (duplicate CredentialNFT import) / consolidate cleanly
• Remove CredentialMetadata from the import
• File compiles without errors
• No unused import warnings from ESLint/TypeScript

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