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/pages/Dashboard.tsx

@@ -1,9 +1,8 @@
 import { useTranslation } from 'react-i18next';
 import { StatCard } from '@/components/shared/StatCard';
 import { ActivityFeed, ActivityItem } from '@/components/shared/ActivityFeed';
-import { DashboardGrid } from '@/components/dashboard/DashboardGrid';
+import { DashboardBuilder } from '@/components/dashboard/DashboardBuilder';
 import { useUnifiedContacts, useAuditLog } from '@/api/hooks';
-import { useDashboardWidgets } from '@/api/dashboard';
 import { useSystemDashboard } from '@/api/systemDashboard';
 import { useAuthStore } from '@/store/authStore';
 import { formatDateTime } from '@/utils/date';
@@ -14,7 +13,6 @@ export function DashboardPage() {
   const { data: companiesData } = useUnifiedContacts(1, 1, undefined, 'company');
   const { data: contactsData } = useUnifiedContacts(1, 1, undefined, 'person');
   const { data: auditData, isError: auditError } = useAuditLog(1, 5);
-  const { data: widgetsData, isError: widgetsError } = useDashboardWidgets();
   const { data: systemData } = useSystemDashboard();
   const user = useAuthStore((s) => s.user);
   const isAdmin = user?.is_system_admin ?? false;
@@ -49,12 +47,15 @@ export function DashboardPage() {
         avatarUrl: null,
       }));
 
-  const widgets = widgetsData?.items ?? [];
-
   return (
     <div className="p-6 max-w-7xl mx-auto" data-testid="dashboard-page">
       <h1 className="text-2xl font-bold text-secondary-900 mb-6">{t('dashboard.title')}</h1>
 
+      {/* Personal dashboard builder (Phase M3) — replaces the old plugin widget grid */}
+      <div className="mb-10">
+        <DashboardBuilder />
+      </div>
+
       <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 mb-8">
         <StatCard
           label={t('dashboard.totalCompanies')}
@@ -78,7 +79,7 @@ export function DashboardPage() {
         />
       </div>
 
-      {/* System Metrics (Admin only) — I-DASH, I-COST, I-USE */}
+      {/* System Metrics (Admin only) — I-DASH, I-COST, I-USE (M4: becomes system MiniApp) */}
       {isAdmin && systemData && (
         <div className="mb-8">
           <h2 className="text-lg font-semibold text-secondary-800 mb-4">{t('dashboard.systemMetrics', 'System Status')}</h2>
@@ -144,18 +145,6 @@ export function DashboardPage() {
         </div>
       )}
 
-      {/* Dynamic Plugin Widgets */}
-      {widgetsError ? (
-        <p className="text-sm text-secondary-500 mb-6" data-testid="dashboard-widgets-unavailable">
-          {t('dashboard.widgetsUnavailable')}
-        </p>
-      ) : widgets.length > 0 ? (
-        <div className="mb-8">
-          <h2 className="text-lg font-semibold text-secondary-800 mb-4">{t('dashboard.widgets')}</h2>
-          <DashboardGrid widgets={widgets} />
-        </div>
-      ) : null}
-
       {auditError ? (
         <p className="text-sm text-secondary-500" data-testid="activity-unavailable">
           {t('dashboard.activityUnavailable')}