✨ Add ScrollArea and Scrollbar components for enhanced scroll functionality

src/components/ui/scroll-area/scroll-area-scrollbar.svelte

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+<script lang="ts">
+  import { ScrollArea as ScrollAreaPrimitive } from "bits-ui";
+  import { cn, type WithoutChild } from "@/utils/cn";
+  import { useHasPrimaryTouch } from "@/hooks/use-has-primary-touch";
+
+  let {
+    ref = $bindable(null),
+    class: className,
+    orientation = "vertical",
+    children,
+    thumbClassName,
+    ...restProps
+  }: WithoutChild<ScrollAreaPrimitive.ScrollbarProps> & {
+    thumbClassName?: string;
+  } = $props();
+
+  const hasPrimaryTouch = useHasPrimaryTouch();
+</script>
+
+{#if !$hasPrimaryTouch}
+  <ScrollAreaPrimitive.Scrollbar
+    bind:ref
+    data-slot="scroll-area-scrollbar"
+    {orientation}
+    class={cn(
+      "flex touch-none p-px transition-[colors] duration-150 select-none hover:bg-neutral-200 data-[state=hidden]:animate-out data-[state=hidden]:fade-out-0 data-[state=visible]:animate-in data-[state=visible]:fade-in-0 dark:hover:bg-neutral-900",
+      orientation === "vertical" &&
+        "h-full w-2.5 border-l border-l-transparent",
+      orientation === "horizontal" &&
+        "h-2.5 flex-col border-t border-t-transparent px-1 pr-1.25",
+      className,
+    )}
+    {...restProps}
+  >
+    {@render children?.()}
+    <ScrollAreaPrimitive.Thumb
+      data-slot="scroll-area-thumb"
+      class={cn(
+        "relative my-0.5 flex-1 rounded-full bg-neutral-300 transition-colors ease-out hover:bg-neutral-500/50 active:bg-neutral-500/75 dark:bg-neutral-800 dark:hover:bg-neutral-700 dark:active:bg-neutral-600",
+        thumbClassName,
+      )}
+    />
+  </ScrollAreaPrimitive.Scrollbar>
+{/if}

src/components/ui/scroll-area/scroll-area.svelte

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+<script lang="ts">
+  import { cn, type WithoutChild } from "@/utils/cn";
+  import { ScrollArea as ScrollAreaPrimitive } from "bits-ui";
+  import { Scrollbar } from "./index.js";
+  import ScrollAreaMask from "./scroll-area-mask.svelte";
+  import { useHasPrimaryTouch } from "@/hooks/use-has-primary-touch";
+
+  type Mask = {
+    top: boolean;
+    bottom: boolean;
+    left: boolean;
+    right: boolean;
+  };
+
+  let {
+    ref = $bindable(null),
+    class: className,
+    orientation = "vertical",
+    scrollbarXClasses = "",
+    scrollbarYClasses = "",
+    children,
+    scrollHideDelay = 0,
+    maskHeight = 30,
+    maskClassName = "",
+    viewportClassName = "",
+    ...restProps
+  }: WithoutChild<ScrollAreaPrimitive.RootProps> & {
+    orientation?: "vertical" | "horizontal" | "both" | undefined;
+    scrollbarXClasses?: string | undefined;
+    scrollbarYClasses?: string | undefined;
+    maskHeight?: number;
+    maskClassName?: string;
+    viewportClassName?: string;
+  } = $props();
+
+  let viewportRef: HTMLDivElement | null = $state(null);
+  const showMask = $state<Mask>({
+    top: true,
+    bottom: true,
+    left: true,
+    right: true,
+  });
+
+  const hasPrimaryTouchStore = useHasPrimaryTouch();
+
+  const checkScrollability = () => {
+    const element = viewportRef;
+    if (!element) {
+      return;
+    }
+
+    const {
+      scrollTop,
+      scrollLeft,
+      scrollWidth,
+      clientWidth,
+      scrollHeight,
+      clientHeight,
+    } = element;
+
+    showMask.top = scrollTop > 0;
+    showMask.bottom = scrollTop + clientHeight < scrollHeight - 1;
+    showMask.left = scrollLeft > 0;
+    showMask.right = scrollLeft + clientWidth < scrollWidth - 1;
+  };
+
+  $effect(() => {
+    const element = viewportRef;
+    if (!element) {
+      return;
+    }
+
+    const controller = new AbortController();
+    const { signal } = controller;
+
+    const resizeObserver = new ResizeObserver(checkScrollability);
+    resizeObserver.observe(element);
+
+    element.addEventListener("scroll", checkScrollability, { signal });
+    window.addEventListener("resize", checkScrollability, { signal });
+
+    checkScrollability();
+
+    return () => {
+      controller.abort();
+      resizeObserver.disconnect();
+    };
+  });
+</script>
+
+{#if $hasPrimaryTouchStore}
+  <div
+    bind:this={ref}
+    role="group"
+    data-slot="scroll-area"
+    aria-roledescription="scroll area"
+    class={cn("relative overflow-hidden", className)}
+    {...restProps}
+  >
+    <div
+      bind:this={viewportRef}
+      data-slot="scroll-area-viewport"
+      class={cn("size-full overflow-auto rounded-[inherit]", viewportClassName)}
+      tabIndex={0}
+    >
+      {@render children?.()}
+    </div>
+
+    {#if maskHeight > 0}
+      <ScrollAreaMask {showMask} class={maskClassName} {maskHeight} />{/if}
+  </div>
+{:else}
+  <ScrollAreaPrimitive.Root
+    bind:ref
+    {scrollHideDelay}
+    data-slot="scroll-area"
+    class={cn("relative", className)}
+    {...restProps}
+  >
+    <ScrollAreaPrimitive.Viewport
+      bind:ref={viewportRef}
+      data-slot="scroll-area-viewport"
+      class={cn("focus-ring size-full rounded-[inherit]", viewportClassName)}
+    >
+      {@render children?.()}
+    </ScrollAreaPrimitive.Viewport>
+
+    {#if maskHeight > 0}
+      <ScrollAreaMask {maskHeight} class={maskClassName} {showMask} />
+    {/if}
+
+    {#if orientation === "vertical" || orientation === "both"}
+      <Scrollbar orientation="vertical" class={scrollbarYClasses} />
+    {/if}
+
+    {#if orientation === "horizontal" || orientation === "both"}
+      <Scrollbar orientation="horizontal" class={scrollbarXClasses} />
+    {/if}
+    <ScrollAreaPrimitive.Corner />
+  </ScrollAreaPrimitive.Root>
+{/if}