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.

demo/main.js

@@ -0,0 +1,24 @@
+import "slatehtml";
+
+import "slatehtml-ui/icon";
+import "slatehtml-ui/side-bar";
+import "slatehtml-ui/progress";
+import "slatehtml-ui/alert";
+import "slatehtml-ui/divider";
+import "slatehtml-ui/bottom-nav";
+import "slatehtml-ui/bottom-nav-item";
+import "slatehtml-ui/collapse";
+
+import { configure } from "slatehtml-ui/configure";
+import { fontAwesomeSvg } from "slatehtml-ui/icons/fontawesome";
+import { mountDocs } from "../src/index.js";
+import "../src/prose.css";
+import "./site.css";
+
+configure({
+  icons: fontAwesomeSvg,
+  iconSize: "15",
+});
+
+await mountDocs("slate-docs-viewer", { indexUrl: "./index.json" });
+document.documentElement.setAttribute("data-ready", "");