feat(ui): add collapsible sidebar for mobile devices

- Add hamburger menu toggle button in top bar (visible on mobile only)
- Sidebar slides in/out from the left with smooth transition
- Add dark overlay when sidebar is open on mobile
- Close sidebar on overlay click, nav item click, or escape key
- Support RTL languages (sidebar slides from right)
- Add dark theme styles for toggle button
- Responsive breakpoint at 768px

static/css/layout/topbar.css

@@ -20,6 +20,42 @@
 	flex-shrink: 0;
 }
 
+/* Sidebar toggle button (hidden on desktop) */
+.sidebar-toggle {
+	display: none;
+	background: none;
+	border: none;
+	padding: 10px;
+	cursor: pointer;
+	color: #4a5568;
+	border-radius: 8px;
+	transition: background-color 0.2s, color 0.2s;
+	margin-right: 12px;
+	flex-shrink: 0;
+}
+
+.sidebar-toggle:hover {
+	background-color: #f7fafc;
+	color: #ff5e3a;
+}
+
+.sidebar-toggle i {
+	font-size: 20px;
+}
+
+/* Mobile responsive styles for top bar */
+@media (max-width: 768px) {
+	.top-bar {
+		padding: 0 16px;
+	}
+
+	.sidebar-toggle {
+		display: flex;
+		align-items: center;
+		justify-content: center;
+	}
+}
+
 .search-container {
 	flex-grow: 1;
 	max-width: 600px;