chore(docs): eslint migration + extractor updates

Migrate docs to eslint flat config (build-script console override); doc
extractor points at configs/eslint.

docs/app/composables/useMarkdown.ts

@@ -0,0 +1,63 @@
+import { marked } from 'marked';
+
+export interface Heading {
+  depth: number;
+  text: string;
+  id: string;
+}
+
+export function slugHeading(text: string): string {
+  return text
+    .toLowerCase()
+    .replace(/`/g, '')
+    .replace(/[^\w\s-]/g, '')
+    .trim()
+    .replace(/\s+/g, '-');
+}
+
+/** Collect h2/h3 headings for the table of contents. */
+export function extractHeadings(markdown: string): Heading[] {
+  const headings: Heading[] = [];
+  const seen = new Map<string, number>();
+  let inFence = false;
+
+  for (const line of markdown.split('\n')) {
+    if (/^\s*```/.test(line)) {
+      inFence = !inFence;
+      continue;
+    }
+    if (inFence) continue;
+
+    const m = line.match(/^(#{2,3})\s+(.+?)\s*#*$/);
+    if (!m) continue;
+
+    const depth = m[1]!.length;
+    const text = m[2]!.replace(/`/g, '').trim();
+    let id = slugHeading(text);
+    const count = seen.get(id) ?? 0;
+    seen.set(id, count + 1);
+    if (count > 0) id = `${id}-${count}`;
+
+    headings.push({ depth, text, id });
+  }
+
+  return headings;
+}
+
+/** Render markdown to HTML with stable heading ids (matching extractHeadings). */
+export function renderMarkdown(markdown: string): string {
+  const seen = new Map<string, number>();
+
+  const renderer = new marked.Renderer();
+  renderer.heading = function ({ tokens, depth }) {
+    const inner = this.parser.parseInline(tokens);
+    const plain = inner.replace(/<[^>]+>/g, '');
+    let id = slugHeading(plain);
+    const count = seen.get(id) ?? 0;
+    seen.set(id, count + 1);
+    if (count > 0) id = `${id}-${count}`;
+    return `<h${depth} id="${id}">${inner}</h${depth}>\n`;
+  };
+
+  return marked.parse(markdown, { renderer, async: false }) as string;
+}