Port Docs-Viewer to slatehtml as the docs-viewer package.

Replace the classic DOM shell with slate widgets, markdown→slate rendering, and a CI index build that uses build-docs.cjs.

src/index.js

@@ -0,0 +1,73 @@
+/**
+ * docs-viewer — documentation viewer on slatehtml + slatehtml-ui.
+ *
+ *   import "slatehtml";
+ *   import { mountDocs } from "docs-viewer";
+ *   import "docs-viewer/prose.css";
+ *
+ *   await mountDocs(document.querySelector("slate-docs-viewer"));
+ */
+
+import { deferCustomElementDefines } from "slatehtml/umc";
+import { DocsApp, faClassToIconName } from "./app.js";
+import { markdownToSpecs, collectHeadings } from "./markdown/render.js";
+import { EventBus } from "./services/event-bus.js";
+import { IndexService } from "./services/index-service.js";
+import { SearchService } from "./services/search-service.js";
+import { DocumentService } from "./services/document-service.js";
+import { NavigationService } from "./services/navigation-service.js";
+
+const modules = import.meta.glob(["./widgets/*.umc"]);
+
+await deferCustomElementDefines(async () => {
+  await Promise.all(
+    Object.entries(modules).map(async ([path, load]) => {
+      try {
+        await load();
+      } catch (err) {
+        console.error(`[slatehtml-docs] failed to load ${path}`, err);
+      }
+    })
+  );
+});
+
+/**
+ * Mount / start the docs app on a <slate-docs-viewer> (or create one).
+ * @param {ParentNode|string|null} target
+ * @param {{ indexUrl?: string, create?: boolean }} [options]
+ * @returns {Promise<DocsApp>}
+ */
+export async function mountDocs(target = "slate-docs-viewer", options = {}) {
+  let host =
+    typeof target === "string" ? document.querySelector(target) : target;
+
+  if (!host && options.create !== false) {
+    host = document.createElement("slate-docs-viewer");
+    if (options.indexUrl) host.setAttribute("index", options.indexUrl);
+    document.body.appendChild(host);
+  }
+  if (!host) throw new Error("mountDocs: no slate-docs-viewer host found");
+
+  // Wait a frame so UMC Construct/stamp finishes.
+  await Promise.resolve();
+  await new Promise((r) => requestAnimationFrame(() => r()));
+
+  const app = new DocsApp(host, {
+    indexUrl: options.indexUrl || host.getAttribute("index") || "./index.json",
+  });
+  await app.start();
+  host.__docsApp = app;
+  return app;
+}
+
+export {
+  DocsApp,
+  faClassToIconName,
+  markdownToSpecs,
+  collectHeadings,
+  EventBus,
+  IndexService,
+  SearchService,
+  DocumentService,
+  NavigationService,
+};