Standardize impulse and hook events as CloudEvents

[lanycrost]

Summary

Adopt the CloudEvents standard for all impulse and hook events to enable interop with the CNCF ecosystem (Knative Eventing, Argo Events, Tekton Triggers).

Problem

Current event format is BubuStack-specific. This limits interoperability with external systems and makes multi-SDK language parity harder.

Proposed change

• Wrap impulse events in CloudEvents envelope
• Standardize hook events as CloudEvents
• Use CloudEvents metadata for provenance fields (prerequisite for compliance primitives)
• Language-agnostic event contract reduces SDK-specific code (prerequisite for Python/TS SDKs)

Low effort, high strategic value.

References

• Roadmap: https://bubustack.io/docs/community/roadmap (Near-term vision)
• CloudEvents spec: https://cloudevents.io/