Fix header/subtitle FOUC and Simple Mode translations

- Refactor tool page headers to prevent flash of unstyled content (FOUC):
  - Move long SEO titles to visually hidden `<h1>` tags for search engines.
  - Use `<h2>` for visible tool titles with text matching i18n keys.
  - Sync default HTML subtitles with [tools.json]

src/js/utils/simple-mode-footer.ts

@@ -31,7 +31,9 @@ if (__SIMPLE_MODE__) {
     `;
     document.body.appendChild(simpleFooter);
 
-    const langContainer = simpleFooter.querySelector('#simple-mode-lang-switcher');
+    const langContainer = simpleFooter.querySelector(
+      '#simple-mode-lang-switcher'
+    );
     if (langContainer) {
       const switcher = createLanguageSwitcher();
       const dropdown = switcher.querySelector('div[role="menu"]');