feat(N3): Backend respektiert X-Workspace-ID bei Listen — contacts/dms/mail/calendar (#367)

- Core-Resolver resolve_workspace_scope(): Zuweisungs-Check, leere Werte fallen weg; Exemptions System-Admin + workspaces:configure_modules (Editor-Deadlock)
- require_workspace_scope(module_key) FastAPI-Dependency (deps.py)
- expand_folder_scope(): Ordner-Subtree (zyklensicher) für ContactFolder + DMS Folder; scope_uuid_set() fail-closed
- contacts: folder_ids-Subtree + contact_types auf GET /contacts, List-Cache bei aktivem Scope deaktiviert (Cache-Leak-Gefahr)
- dms: folder_ids-Subtree + file_types (semantische Matcher) auf /files, Baum-Reduktion auf /folders
- mail: account_ids auf /mails, /threads, /accounts
- calendar: calendar_ids auf /calendar/entries, /calendars
- Frontend-Defaults: getModuleConfig() im workspaceStore, ContactsList default_saved_view_id, Calendar default_view
- Tests: 21/21 neu (TDD rot→grün), Regression 81 passed, Checker 0, tsc clean, Vitest grün, Build OK

frontend/src/pages/Calendar.tsx

@@ -25,6 +25,7 @@ import { useWindowStore } from '@/store/windowStore';
 import { IcsControls } from '@/components/calendar/IcsControls';
 import { SharingSettings } from '@/components/calendar/SharingSettings';
 import { useCalendarStore, type CalendarViewMode } from '@/store/calendarStore';
+import { useWorkspaceStore } from '@/store/workspaceStore';
 import { usePluginToolbarStore } from '@/store/pluginToolbarStore';
 import { ChevronLeft, ChevronRight, ExternalLink, Info, Plus } from 'lucide-react';
 import { PrintButton } from '@/components/common/PrintButton';
@@ -112,6 +113,18 @@ export function CalendarPage() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, []);
 
+  // N3: workspace default calendar view (admin-defined per workspace).
+  // Applied once when the workspace context provides a default_view;
+  // user view switches stay sticky (only re-applied on workspace change).
+  const workspaceDefaultView = useWorkspaceStore(s => s.getModuleConfig('calendar')?.default_view) as CalendarViewMode | undefined;
+  const activeWorkspaceId = useWorkspaceStore(s => s.activeWorkspaceId);
+  useEffect(() => {
+    if (workspaceDefaultView && ['day', 'week', 'month', 'range'].includes(workspaceDefaultView)) {
+      setViewMode(workspaceDefaultView);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [workspaceDefaultView, activeWorkspaceId]);
+
   // Compute date range based on viewMode
   const range = useMemo(() => {
     if (viewMode === 'month') {

frontend/src/pages/ContactsList.tsx

@@ -5,6 +5,7 @@
  */
 
 import React, { useState, useEffect, useCallback, useMemo } from 'react';
+import { useWorkspaceStore } from '@/store/workspaceStore';
 import { useTranslation } from 'react-i18next';
 import { ResizablePanel } from '@/components/ui/ResizablePanel';
 import { Input } from '@/components/ui/Input';
@@ -331,6 +332,17 @@ export function ContactsListPage() {
     if (activeViewId === id) setActiveViewId(null);
   }, [activeViewId, deleteViewMut]);
 
+  // N3: workspace default saved view — applied once when views are loaded
+  // and the user has not chosen a view yet (admin-defined per workspace).
+  const workspaceDefaultViewId = useWorkspaceStore(s => s.getModuleConfig('contacts')?.default_saved_view_id);
+  const activeWorkspaceId = useWorkspaceStore(s => s.activeWorkspaceId);
+  useEffect(() => {
+    if (activeViewId || !workspaceDefaultViewId || savedViews.length === 0) return;
+    const view = savedViews.find(v => v.id === workspaceDefaultViewId);
+    if (view) applySavedView(view);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [workspaceDefaultViewId, activeWorkspaceId, savedViews]);
+
   // Save current filter configuration — via API
   const handleSaveFilter = useCallback((name: string, filterState: FilterState) => {
     createFilterMut.mutate({ name, entity_type: 'contacts', filter_criteria: filterState as any });