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

app/plugins/builtins/dms/folders_routes.py

@@ -16,7 +16,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.db import get_db
 from app.core.visibility import apply_visibility_filter, check_single_entity_access
-from app.deps import get_current_user, require_permission
+from app.deps import get_current_user, require_permission, require_workspace_scope
 from app.plugins.builtins.dms.common import (
     _parse_uuid,
 )
@@ -35,8 +35,13 @@ async def list_folders(
     parent_id: str | None = None,
     db: AsyncSession = Depends(get_db),
     current_user: dict = Depends(get_current_user),
+    workspace_scope: dict | None = Depends(require_workspace_scope("dms")),
 ):
-    """AC1: GET /api/v1/dms/folders → 200 + folder tree (recursive)."""
+    """AC1: GET /api/v1/dms/folders → 200 + folder tree (recursive).
+
+    Phase N3: an active workspace scope (X-Workspace-ID) reduces the tree to
+    the folder subtree — pure AND-restriction, never a grant.
+    """
     tenant_id = uuid.UUID(current_user["tenant_id"])
 
     # Fetch all non-deleted folders for tenant with visibility filter
@@ -52,6 +57,16 @@ async def list_folders(
     result = await db.execute(query)
     all_folders = result.scalars().all()
 
+    # Phase N3: reduce to the scope subtree (folder_ids dimension)
+    if workspace_scope:
+        from app.services.workspace_scope_service import expand_folder_scope
+
+        scope_folder_ids = workspace_scope.get("folder_ids")
+        if isinstance(scope_folder_ids, list) and scope_folder_ids:
+            subtree = await expand_folder_scope(db, Folder, scope_folder_ids)
+            allowed = subtree or set()
+            all_folders = [f for f in all_folders if f.id in allowed]
+
     # Build lookup map
     folder_map: dict[uuid.UUID, dict] = {}
     for f in all_folders: