ui: adjust toolbar heights and icon sizes, remove duplicate AI icon

- TopBar: h-16 → h-[58px] (10% lower), icons w-5 → w-4
- PluginToolbar: min-h-[36px] → min-h-[43px] (20% higher), icons w-3.5 → w-4
- Remove duplicate AI computer icon from TopBar (AISidebar collapsed icon remains)
- Clean up unused imports (toggleAISidebar, aiSidebarCollapsed)

frontend/src/components/layout/AISidebar.tsx

@@ -41,7 +41,7 @@ export function AISidebar() {
           aria-label="KI Assistent öffnen"
           title="KI Assistent"
         >
-          <svg className="w-5 h-5 text-secondary-600" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
+          <svg className="w-4 h-4 text-secondary-600" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
             <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9.75 17L9 20l-1 1h8l-1-1-.75-3M3 13h18M5 17h14a2 2 0 002-2V5a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z" />
           </svg>
         </button>

frontend/src/components/layout/PluginToolbar.tsx

@@ -14,7 +14,7 @@ function ToolbarButton({ item }: { item: ToolbarItem }) {
       `}
       title={item.label}
     >
-      {item.icon && <span className="w-3.5 h-3.5 flex-shrink-0">{item.icon}</span>}
+      {item.icon && <span className="w-4 h-4 flex-shrink-0">{item.icon}</span>}
       <span className="hidden sm:inline">{item.label}</span>
     </button>
   );
@@ -66,7 +66,7 @@ export function PluginToolbar() {
 
   return (
     <div
-      className="flex items-center gap-1 px-2 sm:px-3 py-1 bg-white border-b border-secondary-200 min-h-[36px] overflow-x-auto"
+      className="flex items-center gap-1 px-2 sm:px-3 py-1.5 bg-white border-b border-secondary-200 min-h-[43px] overflow-x-auto"
       data-testid="plugin-toolbar"
     >
       {groupNames.map((groupName, gi) => (

frontend/src/components/layout/TopBar.tsx

@@ -15,7 +15,7 @@ export function TopBar() {
   const { t } = useTranslation();
   const navigate = useNavigate();
   const { user } = useAuthStore();
-  const { toggleSidebar, toggleAISidebar, openAISidebarProactive, aiSidebarCollapsed } = useUIStore();
+  const { toggleSidebar, openAISidebarProactive } = useUIStore();
   const { currentTenant, availableTenants, switchTenant, isSwitching } = useTenant();
   const logoutMutation = useLogout();
 
@@ -54,7 +54,7 @@ export function TopBar() {
 
   return (
     <header
-      className="h-16 bg-white border-b border-secondary-200 flex items-center justify-between px-4 sticky top-0 z-20"
+      className="h-[58px] bg-white border-b border-secondary-200 flex items-center justify-between px-4 sticky top-0 z-20"
       role="banner"
       data-testid="topbar"
     >
@@ -65,26 +65,11 @@ export function TopBar() {
           aria-label="Seitenleiste ein-/ausklappen"
           aria-expanded={true}
         >
-          <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
+          <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
             <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M4 6h16M4 12h16M4 18h16" />
           </svg>
         </button>
 
-        {/* AI Assistant toggle */}
-        <button
-          onClick={toggleAISidebar}
-          className={clsx(
-            'p-2 rounded-md min-h-touch min-w-touch flex items-center justify-center focus:outline-none focus-visible:ring-2 focus-visible:ring-primary-500',
-            aiSidebarCollapsed ? 'hover:bg-secondary-100' : 'bg-primary-50 text-primary-600 hover:bg-primary-100',
-          )}
-          aria-label="KI Assistent"
-          title="KI Assistent"
-        >
-          <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
-            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9.75 17L9 20l-1 1h8l-1-1-.75-3M3 13h18M5 17h14a2 2 0 002-2V5a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z" />
-          </svg>
-        </button>
-
         {/* Tenant switcher */}
         <div ref={tenantRef} className="relative">
           <button
@@ -153,7 +138,7 @@ export function TopBar() {
             aria-label={t('topbar.notifications')}
             aria-expanded={notifOpen}
           >
-            <svg className="w-5 h-5 text-secondary-600" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
+            <svg className="w-4 h-4 text-secondary-600" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
               <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M15 17h5l-1.405-1.405A2.032 2.032 0 0118 14.158V11a6.002 6.002 0 00-4-5.659V5a2 2 0 10-4 0v.341C7.67 6.165 6 8.388 6 11v3.159c0 .538-.214 1.055-.595 1.436L4 17h5m6 0v1a3 3 0 11-6 0v-1m6 0H9" />
             </svg>
             <Badge variant="danger" className="absolute -top-1 -right-1 px-1.5 py-0">3</Badge>