fix(UI-1): add hamburger button and mobile nav drawer -- users can now navigate on screens narrower than 768px

frontend/css/components.css

@@ -618,3 +618,28 @@
   #app-main div[style*='grid-template-columns: 1fr 340px'] {
   }
 }
+
+/* UI-1 FIX: hamburger button and mobile navigation drawer */
+@media (max-width: 768px) {
+  .navbar__hamburger { display: block !important; }
+  .navbar__nav {
+    display: none;
+    position: fixed;
+    top: 60px;
+    left: 0;
+    right: 0;
+    background: var(--bg-secondary);
+    border-bottom: 1px solid var(--border-color);
+    padding: var(--space-4);
+    z-index: 490;
+    flex-direction: column;
+    gap: var(--space-2);
+  }
+  .navbar__nav--open {
+    display: flex !important;
+  }
+  .navbar__nav-link {
+    padding: var(--space-3) var(--space-4);
+    border-radius: var(--radius-md);
+  }
+}

frontend/index.html

@@ -33,7 +33,7 @@
           </div>
         </a>
 
-        <nav class="navbar__nav" aria-label="Main navigation">
+        <nav id="main-nav" class="navbar__nav" aria-label="Main navigation">
           <a class="navbar__nav-link" data-route="/"
              href="#/" onclick="Router.navigate('/');return false;" data-i18n="nav_home" data-i18n-default="Home">Home</a>
           <a class="navbar__nav-link" data-route="/search"
@@ -44,6 +44,13 @@
              href="#/about" onclick="Router.navigate('/about');return false;" data-i18n="nav_about" data-i18n-default="About">About</a>
         </nav>
 
+        <!-- UI-1 FIX: hamburger button for mobile navigation -->
+        <button id="nav-toggle" class="navbar__hamburger" aria-label="Open navigation"
+                onclick="document.getElementById('main-nav').classList.toggle('navbar__nav--open')"
+                style="display:none;background:none;border:none;cursor:pointer;
+                        padding:8px;color:var(--text-primary);font-size:20px">
+          &#9776;
+        </button>
         <div class="navbar__controls">
           <select id="navbar-lang-select"
                   style="background:var(--bg-tertiary);border:1px solid var(--border-color);