feat(sdk): generate TypeScript/Node.js client from proto

[EngineerProjects]

Summary

Generate a TypeScript gRPC client from nexus.proto and publish it as
an npm package. Covers both Node.js server-side usage and browser usage
via gRPC-Web.

Deliverables

• sdk/typescript/ — generated stubs + typed wrapper
• sdk/typescript/src/client.ts — NexusClient class with full TypeScript types
• sdk/typescript/package.json — publishable as @nexus-engine/client
• README with quickstart for Node.js and browser (gRPC-Web)

NexusClient API (proposed)

import { NexusClient } from "@nexus-engine/client";

const client = new NexusClient({ host: "localhost:50051", apiKey: "..." });

// One-shot
const response = await client.query("Refactor the auth module");
console.log(response.content);

// Streaming
for await (const event of client.stream("Write a TypeScript handler")) {
  if (event.textChunk) process.stdout.write(event.textChunk.text);
}

// Sessions
const session = await client.createSession();
await session.submit("First message");

Acceptance criteria

• Generated stubs in sdk/typescript/src/_generated/
• NexusClient exposes a fully typed async/await + async-iterator API
• Works with Node.js 18+ and modern bundlers (Vite, webpack)
• make sdk-typescript regenerates stubs
• At least one working example in sdk/typescript/examples/
• Depends on: feat(grpc): improve proto — sessions, multi-agent RPCs, structured events #17 (improved proto with sessions)