feat(M3): Dashboard-Builder — Edit-Modus, Drag&Drop, Palette, Tabs (#361)

- DashboardBuilder: @dnd-kit 12-Spalten-Flow-Grid (seed-konsistent), View/Edit-Schalter, Resize, Tab-Verwaltung, Dashboard-CRUD + Set-Default, Dirty-Save
- MiniAppHost ersetzt DashboardWidgetLoader (lazy Registry + settings-Props); Palette nur renderbare Apps (component-Filter)
- WidgetSettingsForm generisch aus settings_schema; Bestands-Widgets settings-fähig (RecentContacts: limit)
- api/miniapps.ts + api/dashboards.ts (TanStack-Query-Hooks, documents.ts-Muster)
- Dashboard.tsx = Builder-Host (StatCards/SystemMetrics bleiben bis M4); Legacy-Grid/Loader gelöscht, Geister-Test ersetzt
- Tests: Builder 13/13, Page 11/11, i18n de/en, tsc clean, build OK

frontend/src/components/dashboard/TasksSummaryWidget.tsx

@@ -4,10 +4,11 @@
 
 import React from 'react';
 import { useTranslation } from 'react-i18next';
+import type { WidgetComponentProps } from '@/components/dashboard/MiniAppHost';
 import { useTasks } from '@/api/tasks';
 import { CheckSquare, AlertCircle, Clock } from 'lucide-react';
 
-export function TasksSummaryWidget() {
+export function TasksSummaryWidget({ settings }: WidgetComponentProps) {
   const { t } = useTranslation();
   const { data, isLoading, isError } = useTasks(1, 100);