fix: resolve all 12 TypeScript errors (tsc --noEmit clean)

- mail.ts: add explicit types to decodeMimeHeader callback params
- SessionList.tsx: use React.MouseEvent instead of nativeEvent
- ComposeModal.tsx: construct name from first_name + last_name
- MailDetail.tsx: destructure onReply/onForward from props
- RichTextEditor.tsx: use SetContentOptions object instead of boolean
- MailSearchBar.tsx: add optional value prop to interface
- EmptyState.tsx: add optional children prop
- Badge.tsx: add secondary variant to BadgeVariant, variantClasses, dotColors
- ConfirmDialog.tsx: add optional children prop
- hooks.ts: extend SearchResult type to include mail/file/event

frontend/src/components/ui/EmptyState.tsx

@@ -8,6 +8,7 @@ export interface EmptyStateProps {
   icon?: React.ReactNode;
   action?: React.ReactNode;
   className?: string;
+  children?: React.ReactNode;
 }
 
 export function EmptyState({