Fix verification and revocation issues (#1336, #1337, #1339)

[Ummi-001]

Summary

This PR addresses three issues related to document verification and revocation:

#1336: Submit endpoint doesn't verify the hash against the Stellar anchor

• Modified in to verify the document hash exists on Stellar after anchoring before marking the verification as CONFIRMED
• If verification fails, the record is marked as FAILED instead of CONFIRMED

#1337: Verify endpoint has no caching layer

• Integrated into
• Responses are now cached by document hash to avoid repeated Stellar network calls

#1339: Revoked and deleted documents look identical in responses

• Added field to verify endpoint responses
• Clients can now distinguish between:
  • Never submitted (documentStatus: null)
  • Submitted but not verified (documentStatus: PENDING/ANALYZING/FLAGGED)
  • Verified and active (documentStatus: VERIFIED)
  • Revoked (documentStatus: REJECTED)

Testing

• All existing tests pass
• Manual verification of caching behavior
• Verified that failed anchoring creates FAILED verification record

Closes #1336
Closes #1337
Closes #1338
Closes #1339

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[mftee]

Reviewed. Verifying the document hash against the Stellar anchor before marking a submission CONFIRMED (falling back to FAILED on mismatch) closes a real trust gap — previously the endpoint appears to have trusted the anchoring call succeeding without confirming the hash was actually recorded on-chain. Caching verify responses by document hash avoids redundant Stellar network calls for repeat lookups. Adding documentStatus to the verify response so clients can distinguish never-submitted / pending / verified / revoked is a meaningful API improvement — revoked and deleted previously looked identical to callers. Found and fixed one real issue: an unused DocumentStatus import in verification.controller.ts that was failing the repo's lint check specifically for this file (separate from the broader pre-existing lint debt across the codebase). Approving.