feat: setup full Next.js toolchain and core dependencies

- Add runtime deps: react-query, react-hook-form+zod, zustand, ky, openapi-fetch,
  better-auth, react-markdown, shiki, recharts, next-themes, nuqs, sonner, cmdk,
  vaul, embla-carousel-react, motion, date-fns, tailwind-merge, clsx, cva
- Add dev tooling: vitest, testing-library, playwright, prettier(+tailwind plugin),
  husky, lint-staged, jsdom
- Wire providers (QueryClient, Theme, NuqsAdapter, Tooltip, Sonner) into layout
- Add vitest/playwright/prettier configs + lint-staged pre-commit hook
- Add lib/query-client + lib/http (ky) helpers and sample unit test
- Fix react-hooks/set-state-in-effect lint errors (use-mobile useSyncExternalStore,
  carousel async init)
- Remove committed Next-generated types/ duplicates (regenerated under .next/types)

components/ui/button-group.tsx

@@ -0,0 +1,78 @@
+import { mergeProps } from "@base-ui/react/merge-props";
+import { useRender } from "@base-ui/react/use-render";
+import { cva, type VariantProps } from "class-variance-authority";
+import { cn } from "cn";
+
+import { Separator } from "@/components/ui/separator";
+
+const buttonGroupVariants = cva(
+  "flex w-fit items-stretch *:focus-visible:relative *:focus-visible:z-10 has-[>[data-slot=button-group]]:gap-2 has-[select[aria-hidden=true]:last-child]:[&>[data-slot=select-trigger]:last-of-type]:rounded-r-lg [&>[data-slot=select-trigger]:not([class*='w-'])]:w-fit [&>input]:flex-1",
+  {
+    variants: {
+      orientation: {
+        horizontal:
+          "*:data-slot:rounded-r-none [&>[data-slot]:not(:has(~[data-slot]))]:rounded-r-lg! [&>[data-slot]~[data-slot]]:rounded-l-none [&>[data-slot]~[data-slot]]:border-l-0",
+        vertical:
+          "flex-col *:data-slot:rounded-b-none [&>[data-slot]:not(:has(~[data-slot]))]:rounded-b-lg! [&>[data-slot]~[data-slot]]:rounded-t-none [&>[data-slot]~[data-slot]]:border-t-0",
+      },
+    },
+    defaultVariants: {
+      orientation: "horizontal",
+    },
+  }
+);
+
+function ButtonGroup({
+  className,
+  orientation,
+  ...props
+}: React.ComponentProps<"div"> & VariantProps<typeof buttonGroupVariants>) {
+  return (
+    <div
+      role="group"
+      data-slot="button-group"
+      data-orientation={orientation}
+      className={cn(buttonGroupVariants({ orientation }), className)}
+      {...props}
+    />
+  );
+}
+
+function ButtonGroupText({ className, render, ...props }: useRender.ComponentProps<"div">) {
+  return useRender({
+    defaultTagName: "div",
+    props: mergeProps<"div">(
+      {
+        className: cn(
+          "flex items-center gap-2 rounded-lg border bg-muted px-2.5 text-sm font-medium [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4",
+          className
+        ),
+      },
+      props
+    ),
+    render,
+    state: {
+      slot: "button-group-text",
+    },
+  });
+}
+
+function ButtonGroupSeparator({
+  className,
+  orientation = "vertical",
+  ...props
+}: React.ComponentProps<typeof Separator>) {
+  return (
+    <Separator
+      data-slot="button-group-separator"
+      orientation={orientation}
+      className={cn(
+        "relative self-stretch bg-input data-horizontal:mx-px data-horizontal:w-auto data-vertical:my-px data-vertical:h-auto",
+        className
+      )}
+      {...props}
+    />
+  );
+}
+
+export { ButtonGroup, ButtonGroupSeparator, ButtonGroupText, buttonGroupVariants };