useReq() writes to console.error unconditionally

`useReq()` logs every stream error to the console unconditionally
(`src/lib/stores/useReq.ts:88-89`):

```ts
error: (e) => {
console.error(e);
```

This is library-side logging with no way for a consumer to opt out, and with
`retry` at its default of 3 it fires once per attempt. A library should not write to
the host application's console without being asked to.

Determined by code reading.

## Direction

Remove it, or route it through an opt-in diagnostics channel that the consumer
subscribes to.

Start in src/lib/stores/useReq.ts at lines 88-89 and read how the stream error callback interacts with the default retry count. Done means useReq() no longer writes errors to the host console unconditionally, either by removing that logging or by exposing the issue through an opt-in diagnostics channel.

Written by the indexing model from the issue text.