feat: add persistent cookie sidebar

components/ui/sidebar.tsx

@@ -70,9 +70,22 @@ const SidebarProvider = React.forwardRef<
     const isMobile = useIsMobile();
     const [openMobile, setOpenMobile] = React.useState(false);
 
+    // Read initial state from cookie
+    const initialState = React.useMemo(() => {
+      if (typeof window === "undefined") return defaultOpen;
+      const cookie = document.cookie
+        .split("; ")
+        .find((row) => row.startsWith(SIDEBAR_COOKIE_NAME));
+      if (cookie) {
+        const value = cookie.split("=")[1];
+        return value === "true";
+      }
+      return defaultOpen;
+    }, [defaultOpen]);
+
     // This is the internal state of the sidebar.
     // We use openProp and setOpenProp for control from outside the component.
-    const [_open, _setOpen] = React.useState(defaultOpen);
+    const [_open, _setOpen] = React.useState(initialState);
     const open = openProp ?? _open;
     const setOpen = React.useCallback(
       (value: boolean | ((value: boolean) => boolean)) => {