feat: add useUITree hook for external patch sources

[dflantz]

useUITree Hook

Overview

This MR adds a new hook for iteratively managing UI tree state when patches come from external sources rather than a dedicated fetch endpoint.

Motivation

The existing useUIStream hook is tightly coupled to its own fetch lifecycle:

const { tree, send } = useUIStream({ api: "/api/generate" });
send("Create a dashboard"); // fetches from /api/generate

The use case I am working on relies on supporting patches from non-api sources and iterating on an existing tree without incurring a full regeneration.

API

import { useUITree } from "@json-render/react";
import type { JsonPatch } from "@json-render/core";

function Dashboard() {
  const { tree, applyPatch, setTree, clear } = useUITree();

  // Apply patches from your stream
  const handlePatch = (patch: JsonPatch) => {
    applyPatch(patch);
  };

  return <Renderer tree={tree} registry={registry} />;
}

Notes

• This would be 90% unnecessary if applyPatch was exported, but I wasn't sure if that change would be pattern-breaking / if it is better practice to expose a hook here

• I purposefully avoided making changes to useUIStream() to reduce scope, but if there is appetite for consolidating the tree management layer into its own exportable primitive and reusing it within useUIStream() I'm happy to work on that too.

(Also happy to help with docs if this ends up being considered)

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