feat(tasks): greyed-out "add task" with a hint for list-only columns in "Alle Aufgaben"

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

frontend/src/features/triage/TasksView.tsx

@@ -3138,13 +3138,25 @@ export const TasksView: React.FC<TasksViewProps> = ({
                     )}
                   </div>
 
-                  {/* Quick Add Task to Column */}
-                  {!isSelectedListReadOnly && activeColumns.some((c) => boardIdOf(c) === col.id) && (
-                  <div className="p-2 border-t border-border bg-panel">
+                  {/* Quick Add Task to Column. In "Alle Aufgaben" a new task has no list: a column only lists
+                      have shows the button greyed out, with a hint where the column is */}
+                  {!isSelectedListReadOnly && (
+                  <div
+                    className="p-2 border-t border-border bg-panel"
+                    title={
+                      activeColumns.some((c) => boardIdOf(c) === col.id)
+                        ? undefined
+                        : `Neue Aufgaben hier landen ohne Liste, und dort gibt es diese Spalte nicht. Zum Anlegen die Liste öffnen: ${safeTaskLists
+                            .filter((l) => (Array.isArray(l.columns) ? l.columns : []).some((c) => boardIdOf(c) === col.id))
+                            .map((l) => `„${l.title}“`)
+                            .join(', ')}`
+                    }
+                  >
                     <button
                       type="button"
+                      disabled={!activeColumns.some((c) => boardIdOf(c) === col.id)}
                       onClick={() => handleQuickAddTaskToColumn(col.id)}
-                      className="w-full h-7 px-2 text-xs border border-dashed border-border rounded-btn text-muted hover:text-main hover:bg-canvas flex items-center justify-center gap-1 transition-colors"
+                      className="w-full h-7 px-2 text-xs border border-dashed border-border rounded-btn text-muted hover:text-main hover:bg-canvas flex items-center justify-center gap-1 transition-colors disabled:opacity-40 disabled:pointer-events-none"
                     >
                       <Plus className="w-3 h-3" />
                       <span>Aufgabe hinzufügen</span>