feat(ui): breadcrumb (Space › parent › page) + export menu (md/txt/html/pdf) on pages & spaces

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/components/breadcrumb.js

@@ -0,0 +1,35 @@
+// Inline stylised breadcrumb: Space › parent page › … › current.
+// Walks page.parent_id upward (capped); fills in async, returns the element now.
+import { el } from '../dom.js';
+import { api } from '../api.js';
+
+export function breadcrumb(page) {
+  const nav = el('nav', { class: 'crumbs' });
+  (async () => {
+    const parts = [];
+    try {
+      const sp = await api.get('/api/spaces/' + page.space_id);
+      parts.push({ label: sp.name, href: '#/space/' + sp.id });
+    } catch { /* */ }
+
+    const chain = [];
+    let pid = page.parent_id, guard = 0;
+    while (pid && guard++ < 8) {
+      try {
+        const par = await api.get('/api/pages/' + pid);
+        chain.unshift({ label: par.title, href: '#/page/' + par.id });
+        pid = par.parent_id;
+      } catch { break; }
+    }
+    parts.push(...chain, { label: page.title, href: null });
+
+    nav.replaceChildren();
+    parts.forEach((p, i) => {
+      if (i) nav.appendChild(el('span', { class: 'crumb-sep' }, '›'));
+      nav.appendChild(p.href
+        ? el('a', { class: 'crumb', href: p.href }, p.label)
+        : el('span', { class: 'crumb current' }, p.label));
+    });
+  })();
+  return nav;
+}