feat(inspect-ui): hierarchy + html panels in run detail

HierarchyPanel renders the captured DOM/AX tree with a filter input.
HtmlPanel renders the per-step HTML in an iframe (sandboxed) with a
toggle to view source. HTML tab only shows when the step actually has
HTML captured.

inspect-ui/src/panels/HtmlPanel.tsx

@@ -0,0 +1,73 @@
+import { useEffect, useState } from "react";
+import { htmlUrl } from "../api";
+import "./HtmlPanel.css";
+
+interface HtmlPanelProps {
+  runId: string;
+  fileName: string;
+  available: boolean;
+}
+
+type ViewMode = "render" | "source";
+
+export default function HtmlPanel({ runId, fileName, available }: HtmlPanelProps): JSX.Element {
+  const [mode, setMode] = useState<ViewMode>("render");
+  const [source, setSource] = useState<string | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const url = htmlUrl(runId, fileName);
+
+  useEffect(() => {
+    if (!available || mode !== "source") return;
+    let cancelled = false;
+    setSource(null);
+    setError(null);
+    fetch(url)
+      .then((response) => {
+        if (!response.ok) throw new Error(`${response.status} ${response.statusText}`);
+        return response.text();
+      })
+      .then((text) => {
+        if (!cancelled) setSource(text);
+      })
+      .catch((failure: unknown) => {
+        if (!cancelled) setError(failure instanceof Error ? failure.message : String(failure));
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [available, mode, url]);
+
+  if (!available) {
+    return <div className="html-empty">no html captured for this step</div>;
+  }
+
+  return (
+    <div className="html-panel">
+      <div className="html-toolbar">
+        <button
+          type="button"
+          className={mode === "render" ? "html-tab html-tab-active" : "html-tab"}
+          onClick={() => setMode("render")}
+        >
+          render
+        </button>
+        <button
+          type="button"
+          className={mode === "source" ? "html-tab html-tab-active" : "html-tab"}
+          onClick={() => setMode("source")}
+        >
+          source
+        </button>
+      </div>
+      {mode === "render" ? (
+        <iframe className="html-frame" src={url} sandbox="" title={fileName} />
+      ) : error ? (
+        <div className="html-error">failed to load: {error}</div>
+      ) : source === null ? (
+        <div className="html-empty">loading...</div>
+      ) : (
+        <pre className="html-source">{source}</pre>
+      )}
+    </div>
+  );
+}