feat: select text across bullets and delete it like a text editor; Ctrl+Z in tasks; notes and lists without emoji; custom done columns complete tasks

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/workspace/BacklinksSection.tsx

@@ -84,7 +84,7 @@ export const BacklinksSection: React.FC<BacklinksSectionProps> = ({ docId, title
                 onClick={() => onOpen(l.docId)}
                 className="flex items-center gap-2 min-w-0 max-w-full text-left cursor-pointer group"
               >
-                <span className="shrink-0">{l.icon || '🗒️'}</span>
+                {l.icon && <span className="shrink-0">{l.icon}</span>}
                 <span className="text-sm font-semibold text-main truncate group-hover:text-accent">
                   {l.title || 'Unbenannte Notiz'}
                 </span>