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

.gitignore

@@ -0,0 +1,22 @@
+# Dependencies
+node_modules/
+package-lock.json
+
+# Build outputs
+*.log
+.DS_Store
+Thumbs.db
+
+# IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# Cache
+.cache/
+.sass-cache/
+
+# Temporary files
+*.tmp
+*.temp