frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/components/ui/alert-dialog.tsx

@@ -0,0 +1,134 @@
+"use client";
+
+import * as React from "react";
+import { AlertDialog as AlertDialogPrimitive } from "@base-ui/react/alert-dialog";
+
+import { cn } from "@/lib/utils";
+
+function AlertDialog({ ...props }: AlertDialogPrimitive.Root.Props) {
+  return <AlertDialogPrimitive.Root data-slot="alert-dialog" {...props} />;
+}
+
+function AlertDialogTrigger({ ...props }: AlertDialogPrimitive.Trigger.Props) {
+  return (
+    <AlertDialogPrimitive.Trigger
+      data-slot="alert-dialog-trigger"
+      {...props}
+    />
+  );
+}
+
+function AlertDialogPortal({ ...props }: AlertDialogPrimitive.Portal.Props) {
+  return (
+    <AlertDialogPrimitive.Portal data-slot="alert-dialog-portal" {...props} />
+  );
+}
+
+function AlertDialogOverlay({
+  className,
+  ...props
+}: AlertDialogPrimitive.Backdrop.Props) {
+  return (
+    <AlertDialogPrimitive.Backdrop
+      data-slot="alert-dialog-overlay"
+      className={cn(
+        "fixed inset-0 isolate z-50 bg-black/30 duration-100 supports-backdrop-filter:backdrop-blur-xs data-open:animate-in data-open:fade-in-0 data-closed:animate-out data-closed:fade-out-0",
+        className,
+      )}
+      {...props}
+    />
+  );
+}
+
+function AlertDialogContent({
+  className,
+  ...props
+}: AlertDialogPrimitive.Popup.Props) {
+  return (
+    <AlertDialogPortal>
+      <AlertDialogOverlay />
+      <AlertDialogPrimitive.Popup
+        data-slot="alert-dialog-content"
+        className={cn(
+          "fixed top-1/2 left-1/2 z-50 grid w-full max-w-[calc(100%-2rem)] -translate-x-1/2 -translate-y-1/2 gap-3 rounded-xl bg-popover p-5 text-sm text-popover-foreground ring-1 ring-foreground/10 outline-none data-open:animate-in data-open:fade-in-0 data-open:zoom-in-95 data-closed:animate-out data-closed:fade-out-0 data-closed:zoom-out-95 sm:max-w-md",
+          className,
+        )}
+        {...props}
+      />
+    </AlertDialogPortal>
+  );
+}
+
+function AlertDialogHeader({
+  className,
+  ...props
+}: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-dialog-header"
+      className={cn("flex flex-col gap-1.5", className)}
+      {...props}
+    />
+  );
+}
+
+function AlertDialogFooter({
+  className,
+  ...props
+}: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-dialog-footer"
+      className={cn(
+        "mt-2 flex flex-col-reverse gap-2 sm:flex-row sm:justify-end",
+        className,
+      )}
+      {...props}
+    />
+  );
+}
+
+function AlertDialogTitle({
+  className,
+  ...props
+}: AlertDialogPrimitive.Title.Props) {
+  return (
+    <AlertDialogPrimitive.Title
+      data-slot="alert-dialog-title"
+      className={cn("text-base font-medium leading-none", className)}
+      {...props}
+    />
+  );
+}
+
+function AlertDialogDescription({
+  className,
+  ...props
+}: AlertDialogPrimitive.Description.Props) {
+  return (
+    <AlertDialogPrimitive.Description
+      data-slot="alert-dialog-description"
+      className={cn("text-sm text-muted-foreground", className)}
+      {...props}
+    />
+  );
+}
+
+function AlertDialogClose({ ...props }: AlertDialogPrimitive.Close.Props) {
+  return (
+    <AlertDialogPrimitive.Close data-slot="alert-dialog-close" {...props} />
+  );
+}
+
+export {
+  AlertDialog,
+  AlertDialogClose,
+  AlertDialogContent,
+  AlertDialogDescription,
+  AlertDialogFooter,
+  AlertDialogHeader,
+  AlertDialogOverlay,
+  AlertDialogPortal,
+  AlertDialogTitle,
+  AlertDialogTrigger,
+};