feat: add remote run SDK layer

[roackb2]

Summary

• add explicit @roackb2/heddle/hosted and @roackb2/heddle/remote package entrypoints
• expose the existing ConversationRunService through /hosted without duplicating its implementation
• add a transport-neutral remote run consumer for cursor, duplicate, gap, terminal, and bounded reconnect correctness
• add a runtime protocol codec whose host-supplied schemas define the public activity and result payloads
• migrate Heddle CLI, web, and the hosted-agent example to the same public remote implementation
• document the SDK assumption layers and the remaining host-owned transport, auth, timer, and UI responsibilities

Boundary

This slice deliberately does not choose HTTP, SSE, tRPC, WebSocket, React, authentication, or multi-process delivery. It establishes the reusable hosted and remote domain layers first; concrete transport kits can compose them in a later slice once their residual adapter boundary is clear.

Developer impact

Hosts can now make their assumptions explicit:

import { createConversationEngine } from '@roackb2/heddle'
import { ConversationRunService } from '@roackb2/heddle/hosted'
import {
  ConversationRunConsumerService,
  ConversationRunProtocolCodec,
} from '@roackb2/heddle/remote'

The root ConversationRunService export remains available for compatibility.

Validation

• yarn lint
• yarn typecheck
• yarn test — 635 unit and 290 integration tests
• yarn build
• static package-name import smoke for /hosted and /remote
• npm pack --dry-run --cache /tmp/heddle-npm-cache