Add base templates, theme, and dark mode

assets/theme.js

@@ -0,0 +1,33 @@
+document.addEventListener('DOMContentLoaded', () => {
+  const sidebarToggle = document.getElementById('sidebar-toggle');
+  const themeToggle = document.getElementById('theme-toggle');
+  const root = document.documentElement;
+
+  function setTheme(theme) {
+    root.dataset.theme = theme;
+    localStorage.setItem('theme', theme);
+  }
+  const stored = localStorage.getItem('theme');
+  if (stored) setTheme(stored);
+
+  sidebarToggle?.addEventListener('click', () => {
+    document.body.classList.toggle('sidebar-open');
+  });
+
+  themeToggle?.addEventListener('click', () => {
+    const next = root.dataset.theme === 'dark' ? 'light' : 'dark';
+    setTheme(next);
+  });
+
+  // breadcrumbs
+  const bc = document.getElementById('breadcrumbs');
+  if (bc) {
+    const parts = location.pathname.split('/').filter(Boolean);
+    let path = '';
+    bc.innerHTML = '<a href="/">Home</a>';
+    parts.forEach((p) => {
+      path += '/' + p;
+      bc.innerHTML += ' / <a href="' + path + '">' + p.replace(/-/g, ' ') + '</a>';
+    });
+  }
+});