feat(runtime): résout react/react-dom vers l'instance host pour les layouts plugin

Le runtime SDK expose désormais react/react-dom résolus contre l'instance
hébergée par IdeA plutôt qu'une copie embarquée, pour que les layouts plugin
en JSX/hooks partagent le même arbre React que l'host. hello-plugin migre son
layout d'exemple en .tsx pour illustrer le contrat.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/hello-plugin/src/core/layout.tsx

@@ -0,0 +1,58 @@
+import type { PluginLayoutProps } from "@idea/plugin-sdk";
+import type { ReactElement } from "react";
+import { useMemo, useState } from "react";
+
+let hasLoggedFirstLayoutRender = false;
+
+export function HelloWorldLayout(props: PluginLayoutProps): ReactElement {
+  const [localClicks, setLocalClicks] = useState(0);
+  const hostState = useMemo(() => {
+    return typeof props.state === "object" && props.state !== null && !Array.isArray(props.state)
+      ? (props.state as Record<string, unknown>)
+      : {};
+  }, [props.state]);
+  const persistedClicks =
+    typeof hostState.clicks === "number" && Number.isFinite(hostState.clicks)
+      ? hostState.clicks
+      : 0;
+
+  if (!hasLoggedFirstLayoutRender) {
+    hasLoggedFirstLayoutRender = true;
+    console.info("[hello-plugin] layout first render", {
+      projectId: props.projectId,
+      nodeId: props.nodeId,
+      layoutType: props.layoutType,
+      hasState: props.state !== undefined
+    });
+  }
+
+  return (
+    <section style={{ display: "grid", gap: 12, fontFamily: "system-ui, sans-serif" }}>
+      <header>
+        <h2 style={{ margin: 0, fontSize: 16 }}>Hello Plugin</h2>
+        <p style={{ margin: "4px 0 0", color: "#667085", fontSize: 13 }}>
+          React layout rendered by IdeA host React.
+        </p>
+      </header>
+      <dl style={{ display: "grid", gap: 4, margin: 0, fontSize: 13 }}>
+        <div>
+          <dt style={{ color: "#667085" }}>Project</dt>
+          <dd style={{ margin: 0 }}>{props.projectId}</dd>
+        </div>
+        <div>
+          <dt style={{ color: "#667085" }}>Layout</dt>
+          <dd style={{ margin: 0 }}>{props.layoutType}</dd>
+        </div>
+      </dl>
+      <button
+        type="button"
+        onClick={() => {
+          setLocalClicks((current) => current + 1);
+          props.setState({ ...hostState, clicks: persistedClicks + 1 });
+        }}
+      >
+        Persist click {persistedClicks} / local click {localClicks}
+      </button>
+    </section>
+  );
+}