Refs #3163.
Adds the @codewhale/runtime-sdk workspace with typed fleet Runtime API helpers, protocol-shaped TypeScript declarations, JSON/SSE event fixture handling, and typed RuntimeCapabilityError failures for create/event-stream endpoints that the Rust API has not exposed yet.
Documents the SDK contract in docs/RUNTIME_API.md and wires npm workspace verification through npm test --workspace @codewhale/runtime-sdk.
Hunter B