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/dock.tsx

@@ -29,7 +29,7 @@ const DEFAULT_DISTANCE = 140
 const DEFAULT_DISABLEMAGNIFICATION = false
 
 const dockVariants = cva(
-  "supports-backdrop-blur:bg-white/10 supports-backdrop-blur:dark:bg-black/10 mx-auto mt-8 flex h-[58px] w-max items-center justify-center gap-2 rounded-2xl border p-2 backdrop-blur-md"
+  "mx-auto flex h-[58px] w-max items-center justify-center gap-2 rounded-2xl border border-border bg-background/70 p-2 shadow-lg shadow-black/5 backdrop-blur-md supports-backdrop-blur:bg-background/60 dark:shadow-black/40"
 )
 
 const Dock = React.forwardRef<HTMLDivElement, DockProps>(
@@ -139,8 +139,7 @@ const DockIcon = ({
       ref={ref}
       style={{ width: scaleSize, height: scaleSize, padding }}
       className={cn(
-        "flex aspect-square cursor-pointer items-center justify-center rounded-full",
-        disableMagnification && "hover:bg-muted-foreground transition-colors",
+        "flex aspect-square cursor-pointer items-center justify-center rounded-full transition-colors hover:bg-muted",
         className
       )}
       {...props}