Redesign durable runtime as a companion profile

[callumalpass]

Summary

• replace Runtime Contracts 0.1 with durable Runtime companion profile 0.2
• use the core contract/type/pack model for all record, event, and action contracts
• use CloudEvents and shared action/source/provider declarations from interop 0.1
• add the generated mdbase.runtime.standard pack of ordinary runtime record contracts/types
• define explicit preflight/admission pinning, authorization, recovery, timers, and conformance behavior
• remove the parallel runtime registry, schemas, envelopes, contract mode, and provider-owned definitions
• update the reference packages, official example, specification site, schemas, executable fixtures, and CI drift checks

Verification

• npm test --prefix packages/interop
• cargo test --manifest-path packages/interop-rs/Cargo.toml
• npm test --prefix packages/cel-host
• npm test --prefix packages/runtime-contracts
• npm test --prefix packages/runtime-executor
• python3 scripts/check_v03_tests.py (57 executable, 95 adapter-target tests)
• npm run build --prefix site
• regenerated standard pack has no diff