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.