[CT-22] Build OwnershipChainValidator

[mftee]

Problem

The transfer history for a document is stored in Redis but its integrity is never verified. A gap in the ownership chain (where to_owner of one transfer does not match from_owner of the next) would go undetected, allowing fraudulent transfer insertions.

Proposed Solution

Create an OwnershipChainValidator inside contract/module/ownership-chain/ that verifies the continuity of a document's transfer history.

Acceptance Criteria

• validate_chain(document_hash: &str, cache: &CacheBackend) async function fetches all TransferRecords for the hash and checks continuity
• A chain is valid if each record's from_owner matches the previous record's to_owner
• Returns a ValidationResult enum: Valid, Invalid { gap_at_index: usize, expected_owner: String, found_owner: String }, or Empty (no transfers recorded)
• GET /module/chain/:document_hash endpoint returns the validation result as JSON
• Unit tests cover: empty history, single transfer, valid two-step chain, gap at index 1, and gap at last transfer
• Implementation files live inside contract/module/ownership-chain/