Completes master-cms-module: Build & Test, docs, and appsettings

Finishes the master-cms-module feature (Units 1-4): runs Build and
Test across master-backend, slave-availability-extension and
frontend-cms-page, fixes a missing Availability EF migration for
MasterRegistration and a TanStack Query v5 mutation-callback type
break, adds the missing MasterModule appsettings section, and
documents the module in README.md. Also seeds a tech-debt-backlog
feature to track dead config and pre-existing/introduced frontend
lint findings for later cleanup.

frontend/src/api/useUpdateCmsInstanceStatus.ts

@@ -11,9 +11,9 @@ export function useUpdateCmsInstanceStatus(
     return useMutation<UpdateStatusResult, Error, UpdateVariables>({
         mutationFn: ({ id, ...body }) =>
             api.put<UpdateStatusResult>(`/api/v1/CmsInstances/${id}/status`, body),
-        onSuccess: (data, variables, context) => {
+        onSuccess: (data, variables, ...rest) => {
             queryClient.invalidateQueries({ queryKey: ['cmsInstances'] });
-            options?.onSuccess?.(data, variables, context);
+            options?.onSuccess?.(data, variables, ...rest);
         },
         onError: options?.onError,
     });