chore: temporarily disable Tailwind CSS section

- Comment out Tailwind nav links in header and sidebar
- Comment out Tailwind card on landing page
- Remove tailwind from router SECTIONS array
- Remove tailwind from landing page progress tracking

Tailwind content and styles remain in codebase for easy re-enabling.

src/app.js

@@ -2347,7 +2347,7 @@ function renderFooterLessonLinks() {
  * Update progress indicators on landing page
  */
 function updateLandingProgress() {
-	["css", "html", "tailwind", "markdown"].forEach((sectionId) => {
+	["css", "html", "markdown"].forEach((sectionId) => { // tailwind temporarily disabled
 		const progressEl = document.getElementById(`${sectionId}-progress`);
 		if (progressEl) {
 			const sectionModules = getModulesBySection(lessonEngine.modules, sectionId);