feat: rich text editor, image crop component, empty DB resilience

- RichTextarea with toolbar (Bold, Italic, List, Heading) + Ctrl+B/I
  hotkeys (layout-independent), active state highlighting, preview mode
- Shared ImageCropField component (replaces duplicate in news/classes)
  with drag-to-reposition, Ctrl+scroll zoom, compact layout
- SectionEditor defaultData prop — all admin pages handle empty DB
- Team: section title editable, toast notifications, unsaved data warning
  on navigation (back button, sidebar links, browser close)
- Carousel: continuous card wrapping during drag, edge fade for small teams
- Markup renderer: **bold**, *italic*, ## headings, 🤍 bullet points
- Empty DB guards on all public site sections
- Fix: upload error handling, contact phone field, "team" section key

src/components/sections/MasterClasses.tsx

@@ -220,6 +220,7 @@ function MasterClassCard({
 }
 
 export function MasterClasses({ data, regCounts = {}, popups }: MasterClassesProps) {
+  if (!data?.items?.length) return null;
   const [signupTitle, setSignupTitle] = useState<string | null>(null);
 
   const upcoming = useMemo(() => {