Add TBN v2 verified attestation receipt

[DigiEmu]

Adds the TBN v2 signed attestation receipt for the DigiEmu/VSC interop sample.

Verification result:

• schema_version: tbn-receipt/2.0
• key_id: tbnkey_d9d2b0c3ab2e8aa3
• chain_index: 741
• valid: true

The receipt carries the DigiEmu/VSC manifest hash verbatim as input_hash and preserves the interop boundary:

• DigiEmu/VSC defines the manifest, bundle structure, deterministic hash, and evidence context.
• TBN v2 provides external trust / identity / attestation.
• Neither side recomputes or redefines the other.