feat: add welcome lesson, DVD bounce animation, mobile layout reorder

- Add Welcome module with intro lessons (EN/DE)
- Success message now bounces like DVD screensaver (10s duration)
- Mobile: nav bar at top, preview before editor
- Logo: CODE with purple background pill

src/app.js

@@ -599,11 +599,11 @@ function runCode() {
 		elements.nextBtn.classList.add("success");
 		elements.taskInstruction.classList.add("success-instruction");
 
-		// Show match animation
+		// Show match animation (DVD-style bouncing)
 		elements.previewWrapper?.classList.add("matched");
 		setTimeout(() => {
 			elements.previewWrapper?.classList.remove("matched");
-		}, 2500);
+		}, 10000);
 
 		updateNavigationButtons();
 		updateProgressDisplay();