fix(lessons): style Hello World, add syntax examples, add goodbye module

- Hello World lesson now styles plain text (no h1 required)
- Added syntax examples to CSS Variables, calc(), Media Queries, Flexbox, Grid
- Added goodbye/offboarding module with contribution encouragement

lessons/ar/00-welcome.json

@@ -12,10 +12,10 @@
 			"description": "<strong>Code Crispies</strong> is a free, open-source platform for learning web development through hands-on exercises. No account required!<br><br><strong>What you'll learn:</strong><br>• <strong>HTML</strong> - Semantic elements, forms, tables, SVG (<em>HTML Block & Inline</em>, <em>HTML Forms</em>, <em>HTML Tables</em>)<br>• <strong>CSS</strong> - Selectors, box model, flexbox, animations (<em>CSS Selectors</em>, <em>CSS Box Model</em>, <em>CSS Flexbox</em>)<br>• <strong>Responsive Design</strong> - Media queries and mobile-first layouts<br><br><strong>How it works:</strong><br>1. Read the task in the left panel<br>2. Write code in the editor<br>3. See live results in the preview<br>4. Get instant feedback with hints<br><br><strong>Keyboard shortcuts:</strong> <kbd>Ctrl+Z</kbd> to undo, <kbd>Ctrl+Shift+Z</kbd> to redo<br><br><strong>More resources:</strong><br>• <a href=\"https://nextlevelshit.github.io/html-over-js/\" target=\"_blank\">HTML over JS</a> - Native HTML vs JavaScript solutions<br>• <a href=\"https://nextlevelshit.github.io/web-engineering-mandala/\" target=\"_blank\">Web Engineering Mandala</a> - JavaScript technology roadmap",
 			"task": "Write <code>Hello World</code>",
 			"previewHTML": "",
-			"previewBaseCSS": "body { font-family: system-ui, sans-serif; padding: 20px; text-align: center; } h1 { color: #6366f1; }",
+			"previewBaseCSS": "body { font-family: system-ui, sans-serif; padding: 20px; text-align: center; font-size: 2rem; color: #6366f1; font-weight: bold; }",
 			"sandboxCSS": "",
 			"initialCode": "",
-			"solution": "<h1>Hello World</h1>",
+			"solution": "Hello World",
 			"previewContainer": "preview-area",
 			"validations": [
 				{