fix(mobile): add functional mobile hamburger menu

- Add mobile menu button with hamburger/close icons
- Add full-screen mobile navigation overlay
- Add JavaScript for menu toggle functionality
- Prevent body scroll when menu is open
- Close menu on link click, escape key, or outside click
- Add proper ARIA attributes for accessibility

app/presentation/templates/partials/header.html

@@ -7,10 +7,25 @@
             </svg>
             <span data-testid="logo-text">Blog</span>
         </a>
-        
+
         {% include "partials/nav.html" %}
-        
+
         <div class="header-actions" data-testid="header-actions">
+            <button
+                type="button"
+                class="mobile-menu-btn"
+                data-testid="mobile-menu-toggle"
+                aria-label="Toggle menu"
+                aria-expanded="false"
+                aria-controls="mobile-nav"
+            >
+                <svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg" class="menu-icon-open">
+                    <path d="M3 12h18M3 6h18M3 18h18" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+                </svg>
+                <svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg" class="menu-icon-close" style="display: none;">
+                    <path d="M18 6L6 18M6 6l12 12" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+                </svg>
+            </button>
             <button 
                 type="button" 
                 class="theme-toggle" 
@@ -170,5 +185,153 @@
     .user-name {
         display: none;
     }
+
+    .mobile-menu-btn {
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        width: 2.5rem;
+        height: 2.5rem;
+        padding: 0;
+        background: transparent;
+        border: 1px solid var(--color-border);
+        border-radius: 6px;
+        color: var(--color-text);
+        cursor: pointer;
+        transition: all 0.2s ease;
+    }
+
+    .mobile-menu-btn:hover {
+        background-color: var(--color-hover);
+    }
+
+    .mobile-menu-btn[aria-expanded="true"] {
+        background-color: var(--color-primary);
+        border-color: var(--color-primary);
+        color: var(--color-primary-contrast);
+    }
+
+    .mobile-nav {
+        display: none;
+        position: fixed;
+        top: 4rem;
+        left: 0;
+        right: 0;
+        bottom: 0;
+        background-color: var(--color-body);
+        z-index: 99;
+        padding: 2rem;
+        overflow-y: auto;
+    }
+
+    .mobile-nav.is-open {
+        display: block;
+    }
+
+    .mobile-nav .nav-link {
+        display: block;
+        padding: 1rem 0;
+        font-size: 1.25rem;
+        border-bottom: 1px solid var(--color-border);
+        border-bottom-color: transparent;
+    }
+
+    .mobile-nav .nav-link:last-child {
+        border-bottom: none;
+    }
+}
+
+@media (min-width: 769px) {
+    .mobile-menu-btn {
+        display: none;
+    }
+
+    .mobile-nav {
+        display: none !important;
+    }
 }
 </style>
+
+<!-- Mobile Navigation Menu -->
+<nav class="mobile-nav" id="mobile-nav" data-testid="mobile-nav" aria-label="Mobile navigation">
+    <a href="/" class="nav-link {% if active_page == 'home' %}active{% endif %}" data-testid="mobile-nav-link-home">
+        Home
+    </a>
+    <a href="/posts" class="nav-link {% if active_page == 'posts' %}active{% endif %}" data-testid="mobile-nav-link-posts">
+        Posts
+    </a>
+    <a href="/about" class="nav-link {% if active_page == 'about' %}active{% endif %}" data-testid="mobile-nav-link-about">
+        About
+    </a>
+</nav>
+
+<script>
+(function() {
+    'use strict';
+
+    const menuBtn = document.querySelector('[data-testid="mobile-menu-toggle"]');
+    const mobileNav = document.getElementById('mobile-nav');
+    const menuIconOpen = menuBtn?.querySelector('.menu-icon-open');
+    const menuIconClose = menuBtn?.querySelector('.menu-icon-close');
+
+    function toggleMenu() {
+        if (!mobileNav || !menuBtn) return;
+
+        const isOpen = mobileNav.classList.toggle('is-open');
+        menuBtn.setAttribute('aria-expanded', isOpen ? 'true' : 'false');
+
+        if (menuIconOpen && menuIconClose) {
+            menuIconOpen.style.display = isOpen ? 'none' : 'block';
+            menuIconClose.style.display = isOpen ? 'block' : 'none';
+        }
+
+        // Prevent body scroll when menu is open
+        document.body.style.overflow = isOpen ? 'hidden' : '';
+    }
+
+    function closeMenu() {
+        if (!mobileNav || !menuBtn) return;
+
+        mobileNav.classList.remove('is-open');
+        menuBtn.setAttribute('aria-expanded', 'false');
+
+        if (menuIconOpen && menuIconClose) {
+            menuIconOpen.style.display = 'block';
+            menuIconClose.style.display = 'none';
+        }
+
+        document.body.style.overflow = '';
+    }
+
+    if (menuBtn) {
+        menuBtn.addEventListener('click', function(e) {
+            e.preventDefault();
+            e.stopPropagation();
+            toggleMenu();
+        });
+    }
+
+    // Close menu when clicking on a link
+    if (mobileNav) {
+        mobileNav.querySelectorAll('a').forEach(function(link) {
+            link.addEventListener('click', closeMenu);
+        });
+    }
+
+    // Close menu on escape key
+    document.addEventListener('keydown', function(e) {
+        if (e.key === 'Escape' && mobileNav?.classList.contains('is-open')) {
+            closeMenu();
+        }
+    });
+
+    // Close menu when clicking outside
+    document.addEventListener('click', function(e) {
+        if (mobileNav?.classList.contains('is-open') &&
+            !mobileNav.contains(e.target) &&
+            !menuBtn?.contains(e.target)) {
+            closeMenu();
+        }
+    });
+})();
+</script>