fix(auth): preserve last workspace ID across re-login

The logout handler was clearing `multica_workspace_id` from storage,
so re-login always defaulted to the first workspace. The workspace ID
is a user preference, not session-sensitive data — keep it so both
web and desktop restore the correct workspace after re-authentication.

Also pass `lastWorkspaceId` in the desktop login page, which was
previously missing.

apps/desktop/src/renderer/src/pages/login.tsx

@@ -2,6 +2,8 @@ import { LoginPage } from "@multica/views/auth";
 import { MulticaIcon } from "@multica/ui/components/common/multica-icon";
 
 export function DesktopLoginPage() {
+  const lastWorkspaceId = localStorage.getItem("multica_workspace_id");
+
   return (
     <div className="flex h-screen flex-col">
       {/* Traffic light inset */}
@@ -11,6 +13,7 @@ export function DesktopLoginPage() {
       />
       <LoginPage
         logo={<MulticaIcon bordered size="lg" />}
+        lastWorkspaceId={lastWorkspaceId}
         onSuccess={() => {
           // Auth store update triggers AppContent re-render → shows DesktopShell
         }}

packages/core/auth/store.ts

@@ -72,7 +72,6 @@ export function createAuthStore(options: AuthStoreOptions) {
 
     logout: () => {
       storage.removeItem("multica_token");
-      storage.removeItem("multica_workspace_id");
       api.setToken(null);
       api.setWorkspaceId(null);
       onLogout?.();