Contract: add get_contract_metadata() to TypeScript SDK

[Haroldwonder]

Summary

get_contract_metadata is implemented in the contract and returns ContractMetadata (name, version, description), but the TypeScript SDK TrustLinkClient does not expose it. Integrators who want to display contract info in their UI must use the lower-level bindings.

Acceptance Criteria

• TrustLinkClient.getContractMetadata() is implemented.
• The method is documented in sdk/typescript/README.md.