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/store/workspaceStore.ts

@@ -58,6 +58,7 @@ interface WorkspaceStoreState {
   // Helpers
   isModuleVisible: (moduleKey: string, isSystemAdmin?: boolean) => boolean;
   visibleModuleKeys: () => Set<string>;
+  getModuleConfig: (moduleKey: string) => Record<string, any>;
   hasWorkspaces: () => boolean;
   // Reset
   reset: () => void;
@@ -111,6 +112,14 @@ export const useWorkspaceStore = create<WorkspaceStoreState>()(
         );
       },
 
+      getModuleConfig: (moduleKey: string) => {
+        // N3: scope defaults (e.g. default_saved_view_id, default_view) come
+        // from the active workspace context; no context = no defaults.
+        const ctx = get().context;
+        const mod = (ctx?.modules ?? []).find(m => m.module_key === moduleKey);
+        return mod?.config ?? {};
+      },
+
       hasWorkspaces: () => get().myWorkspaces.length > 0,
 
       reset: () => {