fix(ui): hide scrollbars on mobile, keep styled bars on desktop

Scrollbars on mobile caused layout shift (content pushed left).
Hidden via media query on mobile; desktop retains thin styled scrollbars.
Also removes inline scrollbarWidth override in DayPlanSidebar that bypassed the CSS rule.

client/src/components/Planner/DayPlanSidebar.tsx

@@ -1023,7 +1023,7 @@ const DayPlanSidebar = React.memo(function DayPlanSidebar({
       </div>
 
       {/* Tagesliste */}
-      <div className="scroll-container" style={{ flex: 1, overflowY: 'auto', minHeight: 0, scrollbarWidth: 'thin', scrollbarColor: 'var(--scrollbar-thumb) transparent' }}>
+      <div className="scroll-container" style={{ flex: 1, overflowY: 'auto', minHeight: 0 }}>
         {days.map((day, index) => {
           const isSelected = selectedDayId === day.id
           const isExpanded = expandedDays.has(day.id)

client/src/index.css

@@ -323,7 +323,7 @@ body {
   display: none;
 }
 
-/* Scrollbalken */
+/* Scrollbars — styled on desktop, hidden on mobile */
 ::-webkit-scrollbar {
   width: 6px;
   height: 6px;
@@ -333,21 +333,23 @@ body {
   height: 0;
   width: 0;
 }
-
 ::-webkit-scrollbar-track {
   background: var(--scrollbar-track);
   border-radius: 3px;
 }
-
 ::-webkit-scrollbar-thumb {
   background: var(--scrollbar-thumb);
   border-radius: 3px;
 }
-
 ::-webkit-scrollbar-thumb:hover {
   background: var(--scrollbar-hover);
 }
 
+@media (max-width: 767px) {
+  * { scrollbar-width: none; }
+  ::-webkit-scrollbar { width: 0; height: 0; }
+}
+
 .route-info-pill { background: none !important; border: none !important; box-shadow: none !important; width: auto !important; height: auto !important; margin: 0 !important; }
 .chat-scroll { overflow-y: auto !important; scrollbar-width: none; -webkit-overflow-scrolling: touch; }
 .chat-scroll::-webkit-scrollbar { width: 0; background: transparent; }
@@ -447,11 +449,6 @@ img[alt="TREK"] {
   color-scheme: dark;
 }
 
-/* Scroll-Container */
-.scroll-container {
-  scrollbar-width: thin;
-  scrollbar-color: #d1d5db #f1f5f9;
-}
 
 /* Toast-Animationen */
 @keyframes slideUp {