Mobile polish: max thumbnail quality, tab-bar filter chips, fix vertical split default

- CLSI thumbnails: bump to 794px/q90 (matches preview quality) for
  crisp display on 2x/3x phone screens
- Lumière filter chips → underline tab bar: single scrollable row with
  teal active indicator, no more wrapping alignment issues; zoom buttons
  separated by a vertical divider on the right
- Fix editor vertical split default on mobile: disable react-resizable-panels
  autoSaveId on mobile to prevent a stale collapsed PDF pane from firing
  onCollapse → changeLayout('flat') and overriding the verticalSplit
  default set by getInitialLayout()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/web/frontend/js/features/ide-react/components/layout/main-layout.tsx

@@ -83,7 +83,14 @@ export default function MainLayout() {
               key={isVertical ? 'vertical' : 'horizontal'}
               autoSaveId={
                 isVertical
-                  ? 'ide-redesign-editor-and-pdf-panel-group-vertical'
+                  ? // On mobile, skip autoSave: a stale collapsed PDF pane
+                    // would fire onCollapse → changeLayout('flat'), overriding
+                    // the verticalSplit default from getInitialLayout().
+                    // The pdf.layout localStorage key already persists the
+                    // user's explicit flat/open preference independently.
+                    isMobile
+                    ? null
+                    : 'ide-redesign-editor-and-pdf-panel-group-vertical'
                   : 'ide-redesign-editor-and-pdf-panel-group'
               }
               direction={isVertical ? 'vertical' : 'horizontal'}