Refactor: Replace sidebar with horizontal navigation bar

- Remove sidebar and toggle functionality
- Add Bootstrap navbar with dropdown menus
- Move navigation to top between header and content
- Update menu rendering for Bootstrap dropdowns
- Clean up unused files (header.mustache, sidebar.mustache, sidebar.js)
- Add guide link with book icon in footer
- Simplify layout structure
- Remove duplicate code and fix syntax errors
- Add .gitignore for node_modules and other temp files

public/assets/icon.svg

@@ -0,0 +1,11 @@
+<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
+  <!-- < -->
+  <path d="M8 8 L3 16 L8 24" stroke="#ffffff" stroke-width="3" fill="none" stroke-linecap="round" stroke-linejoin="round"/>
+  
+  <!-- / -->
+  <path d="M12 24 L18 8" stroke="#ffffff" stroke-width="3" stroke-linecap="round"/>
+  
+  <!-- .. -->
+  <circle cx="22" cy="20" r="2" fill="#ffffff"/>
+  <circle cx="28" cy="20" r="2" fill="#ffffff"/>
+</svg>