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/markdown/preprocess.js

@@ -0,0 +1,60 @@
+/**
+ * Frontmatter, wiki links, and wiki image embeds (Docs-Viewer compatible).
+ */
+
+export function extractMetadata(content) {
+  const lines = String(content || "").trim().split("\n");
+  let metadata = {};
+  let contentStart = 0;
+
+  if (lines[0]?.trim() === "---") {
+    const endMetadata = lines.findIndex((line, index) => index > 0 && line.trim() === "---");
+    if (endMetadata !== -1) {
+      const entries = lines
+        .slice(1, endMetadata)
+        .map((line) => line.match(/^([\w-]+):\s*(.*)$/))
+        .filter(Boolean)
+        .map(([, key, value]) => {
+          if (key === "defaultOpen") {
+            return [key, value.trim().toLowerCase() === "true"];
+          }
+          if (key === "sort") return [key, parseInt(value.trim(), 10)];
+          return [key, value.trim()];
+        });
+      metadata = Object.fromEntries(entries);
+      contentStart = endMetadata + 1;
+    }
+  }
+
+  return {
+    metadata,
+    content: lines.slice(contentStart).join("\n").trim(),
+  };
+}
+
+export function ensureTitle(content, title) {
+  const stripped = String(content || "")
+    .replace(/^#\s+.*$/m, "")
+    .trim();
+  return `# ${title}\n\n${stripped}`;
+}
+
+export function processWikiLinks(content, indexService, documents) {
+  return String(content || "").replace(/\[\[(.*?)\]\]/g, (match, linkText) => {
+    const [targetTitle, displayText] = linkText.split("|").map((s) => s.trim());
+    if (/\.(png|jpg|jpeg|gif|webp|mp4|webm)$/i.test(targetTitle)) return match;
+    const doc = indexService.findDocumentByTitle(documents, targetTitle);
+    if (!doc) return match;
+    return `[${displayText || doc.title}](?${doc.slug})`;
+  });
+}
+
+export function processImages(content, _basePath) {
+  return String(content || "").replace(/!\[\[(.*?)\]\]/g, (match, filename) => {
+    const mediaPath = `./docs/images/${filename}`;
+    if (filename.toLowerCase().endsWith(".mp4") || filename.toLowerCase().endsWith(".webm")) {
+      return `\n\n<video src="${mediaPath}" controls playsinline></video>\n\n`;
+    }
+    return `\n\n![${filename}](${mediaPath})\n\n`;
+  });
+}