Expose installable NodeAgent runtime contracts and Pi AI adapter

[HomenShum]

Outcome

Creates a collision-safe package boundary for NodeAgent and a real optional Pi AI provider adapter while keeping orchestration, tools, policy, durability, and receipts inside NodeAgent.

• renames the package to @homenshum/nodeagent
• exports provider-neutral runtime/model/event contracts
• implements nodeagent.event/v1 validation aligned with NodeKit
• implements lazy Pi model lookup, native streaming deltas, structured tool calls, exact usage/cost normalization, and honest error classification
• adds tarball-ready library builds without making Pi mandatory for deterministic mode

Proof

• typecheck passed
• 9 test files / 47 tests passed
• full production build passed
• deterministic/durable/SQLite/happy-path proof passed
• fresh tarball consumer import passed
• npm audit --omit=dev: 0 vulnerabilities

Dependency status

The branch's own verify and security checks pass. The hosted node-platform / conformance check is expected to remain red until the canonical provider/event ownership additions in node-platform #4 land on main; the same assembled registry passes locally.

Boundaries

This does not publish npm, deploy an app, or replace the existing NodeAgent orchestration loop.