Define first-class event and action interoperability

[callumalpass]

What changed

Defines record, event, and action variants of mdbase.contract, plus Event &
Action Interoperability Profile 0.1. Adds CloudEvents envelopes, action
request/invocation/outcome evidence, exact contract resolution, role-specific
conformance, portable TypeScript and Rust packages, schemas, fixtures, and
documentation.

The design keeps record implements entries in type files, while event sources
and action providers declare executable roles at runtime. Events multicast;
actions select exactly one provider; authorization remains separate and
default-deny.

Validation

• v0.3 suite: 55 executable / 111 adapter-target cases
• TypeScript interop: 11/11 tests and build
• Rust interop: 5/5 tests and package verification
• spec site build
• combined with standard JSON Pointer field references