fix(slider): focus thumb on pointerdown for keyboard parity

src/shared/ui/Slider/Slider.stories.svelte

@@ -39,8 +39,6 @@ const { Story } = defineMeta({
 <script lang="ts">
 import type { ComponentProps } from 'svelte';
 let value = $state(50);
-let valueLow = $state(25);
-let valueHigh = $state(75);
 </script>
 
 <Story

src/shared/ui/Slider/Slider.svelte

@@ -88,6 +88,7 @@ const percent = $derived.by(() => {
 });
 
 let trackEl: HTMLElement | undefined = $state();
+let thumbEl: HTMLElement | undefined = $state();
 let dragging = $state(false);
 
 /**
@@ -131,6 +132,7 @@ function handlePointerDown(event: PointerEvent): void {
         return;
     }
     dragging = true;
+    thumbEl?.focus();
     (event.currentTarget as HTMLElement).setPointerCapture?.(event.pointerId);
     seek(event);
 }
@@ -237,6 +239,7 @@ const thumbClasses = `block w-2.5 h-2.5 bg-brand
 
             <span
                 role="slider"
+                bind:this={thumbEl}
                 tabindex={disabled ? -1 : 0}
                 aria-label="Value"
                 aria-orientation="vertical"
@@ -285,6 +288,7 @@ const thumbClasses = `block w-2.5 h-2.5 bg-brand
 
             <span
                 role="slider"
+                bind:this={thumbEl}
                 tabindex={disabled ? -1 : 0}
                 aria-label="Value"
                 aria-orientation="horizontal"

src/shared/ui/Slider/Slider.svelte.test.ts

@@ -149,6 +149,15 @@ describe('Pointer', () => {
         expect(screen.getByRole('slider')).toHaveAttribute('aria-valuenow', '0');
     });
 
+    it('focuses the thumb on pointerdown so arrow keys work immediately', async () => {
+        const { container } = render(Slider, { value: 0, min: 0, max: 100 });
+        const track = container.querySelector('[role="presentation"]') as HTMLElement;
+        track.getBoundingClientRect = () =>
+            ({ left: 0, right: 200, top: 0, bottom: 20, width: 200, height: 20 }) as DOMRect;
+        await fireEvent.pointerDown(track, { clientX: 100, clientY: 10, pointerId: 1 });
+        expect(screen.getByRole('slider')).toBe(document.activeElement);
+    });
+
     it('maps a vertical drag with the inverted axis (bottom→min, top→max)', async () => {
         const { container } = render(Slider, { value: 0, min: 0, max: 100, orientation: 'vertical' });
         const track = container.querySelector('[role="presentation"]') as HTMLElement;