Implement authentication system with access control UI

frontend/src/components/Layout.css

@@ -98,6 +98,170 @@
   opacity: 0.7;
 }
 
+/* Login link */
+.nav-login {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 8px 16px;
+  color: var(--text-primary);
+  font-size: 0.875rem;
+  font-weight: 500;
+  border-radius: var(--radius-md);
+  transition: all var(--transition-fast);
+  margin-left: 8px;
+  border: 1px solid var(--border-primary);
+}
+
+.nav-login:hover {
+  color: var(--text-primary);
+  background: var(--bg-hover);
+  border-color: var(--border-secondary);
+}
+
+/* User Menu */
+.user-menu {
+  position: relative;
+  margin-left: 8px;
+}
+
+.user-menu-trigger {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 6px 12px;
+  background: transparent;
+  border: 1px solid var(--border-primary);
+  border-radius: var(--radius-md);
+  color: var(--text-primary);
+  font-size: 0.875rem;
+  font-weight: 500;
+  cursor: pointer;
+  transition: all var(--transition-fast);
+}
+
+.user-menu-trigger:hover {
+  background: var(--bg-hover);
+  border-color: var(--border-secondary);
+}
+
+.user-avatar {
+  width: 28px;
+  height: 28px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: var(--accent-gradient);
+  border-radius: var(--radius-sm);
+  color: white;
+  font-weight: 600;
+  font-size: 0.8125rem;
+}
+
+.user-name {
+  max-width: 120px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.user-menu-dropdown {
+  position: absolute;
+  top: 100%;
+  right: 0;
+  margin-top: 8px;
+  min-width: 200px;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border-primary);
+  border-radius: var(--radius-md);
+  box-shadow: var(--shadow-lg);
+  z-index: 200;
+  overflow: hidden;
+}
+
+.user-menu-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 12px 16px;
+}
+
+.user-menu-username {
+  font-size: 0.875rem;
+  font-weight: 500;
+  color: var(--text-primary);
+}
+
+.user-menu-badge {
+  padding: 2px 8px;
+  background: var(--accent-gradient);
+  border-radius: 100px;
+  font-size: 0.6875rem;
+  font-weight: 600;
+  color: white;
+  text-transform: uppercase;
+  letter-spacing: 0.02em;
+}
+
+.user-menu-divider {
+  height: 1px;
+  background: var(--border-primary);
+}
+
+.user-menu-item {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  width: 100%;
+  padding: 12px 16px;
+  background: transparent;
+  border: none;
+  color: var(--text-secondary);
+  font-size: 0.875rem;
+  cursor: pointer;
+  transition: all var(--transition-fast);
+  text-align: left;
+  text-decoration: none;
+}
+
+.user-menu-item:hover {
+  background: var(--bg-hover);
+  color: var(--text-primary);
+}
+
+.user-menu-item svg {
+  opacity: 0.7;
+}
+
+.user-menu-item:hover svg {
+  opacity: 1;
+}
+
+/* User menu loading state */
+.user-menu-loading {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 40px;
+  height: 40px;
+  margin-left: 8px;
+}
+
+.user-menu-spinner {
+  width: 16px;
+  height: 16px;
+  border: 2px solid var(--border-secondary);
+  border-top-color: var(--accent-primary);
+  border-radius: 50%;
+  animation: user-menu-spin 0.6s linear infinite;
+}
+
+@keyframes user-menu-spin {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
 /* Main content */
 .main {
   flex: 1;