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

engine/templates/assets/footer.mustache

@@ -0,0 +1,26 @@
+<footer class="bg-light border-top py-3">
+    <div class="container-fluid">
+        <div class="row">
+            <div class="col-md-12">
+                <div class="d-flex justify-content-between align-items-center">
+                    <div class="file-info">
+                        <i class="bi bi-file-text"></i>
+                        <span class="page-title" title="{{page_title}}">{{page_title}}</span>
+                        {{#file_info}}
+                            <span class="file-details"> | {{{file_info}}}</span>
+                        {{/file_info}}
+                    </div>
+                    <div class="site-info">
+                        <small class="text-muted">
+                            <a href="?guide" class="guide-link" title="Handleiding">
+                                <i class="bi bi-book"></i>
+                            </a>
+                            <span class="ms-2">|</span>
+                            Powered by <a href="https://git.noorlander.info/E.Noorlander/CodePress.git" target="_blank" rel="noopener">CodePress CMS</a>
+                        </small>
+                    </div>
+                </div>
+            </div>
+        </div>
+    </div>
+</footer>

engine/templates/assets/navigation.mustache

@@ -0,0 +1,23 @@
+<nav class="navbar navbar-expand-lg navbar-dark bg-primary">
+    <div class="container-fluid">
+        <a class="navbar-brand" href="?page={{default_page}}">
+            <img src="/assets/icon.svg" alt="CodePress Logo" width="32" height="32" class="me-2">
+            {{site_title}}
+        </a>
+        
+        <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
+            <span class="navbar-toggler-icon"></span>
+        </button>
+        
+        <div class="collapse navbar-collapse" id="navbarNav">
+            <ul class="navbar-nav me-auto">
+                {{{menu}}}
+            </ul>
+            
+            <form class="d-flex" method="GET" action="">
+                <input class="form-control me-2" type="search" name="search" placeholder="Search..." value="{{search_query}}">
+                <button class="btn btn-outline-light" type="submit">Search</button>
+            </form>
+        </div>
+    </div>
+</nav>