fix: explicitly disable HTTP/2 in undici Agent to prevent inference hangs

[andreyobsidiam]

Summary

• Explicitly set `allowH2: false` in the undici `Agent` options to guarantee HTTP/1.1
• Prevents HTTP/2 ALPN negotiation which causes upsert requests with Cloud Inference vectors to hang indefinitely inside Docker containers
• Zero behavioral change for normal cases (allowH2 is already false by default); makes the guarantee explicit

Problem

Using `client.upsert()` with inference vectors (`vector: { text, model }`) hangs forever inside Docker containers. The same request via curl HTTP/1.1 completes in ~86ms.

Solution

One-line addition in `packages/js-client-rest/src/dispatcher.ts`:

```ts
new Agent({
// ...
allowH2: false,
})
```

Testing

• Manual test: upsert with inference vectors now completes in ~200ms inside Docker (was: infinite hang)
• Existing unit tests pass (no change to API surface)

Related Issue

Fixes #131