Integration: Cryptographic tool-call receipts from Signet

AgentOps captures the observability side of agent runs well. A complementary layer is cryptographic evidence: proving *what* each tool call sent, *who* signed it, and that the audit trail hasn't been tampered with.

[Signet](https://github.com/Prismer-AI/signet) generates Ed25519-signed receipts for every tool call, chained into a tamper-evident audit log. It already integrates with the same frameworks AgentOps supports (LangChain, CrewAI, OpenAI Agents SDK, Pydantic AI).

A lightweight integration could:
1. Attach the Signet receipt ID to the AgentOps event for cross-referencing
2. Surface signed/unsigned status in the AgentOps dashboard
3. Let users export AgentOps sessions with cryptographic proof attached

Signet is local-first (no SaaS dependency, offline-verifiable), so it wouldn't require users to create accounts with a third party. The receipts are JSON with Ed25519 signatures — straightforward to include as event metadata.

Available as `pip install signet-auth` (Python) and `npm install @signet-auth/core` (TypeScript).

Happy to prototype the integration or discuss what telemetry signals would be most useful.