test(slider): centralize jsdom pointer shims and add vertical drag test

vitest.setup.jsdom.ts

@@ -44,3 +44,20 @@ Object.defineProperty(window, 'localStorage', {
     value: localStorageMock,
     writable: true,
 });
+
+// jsdom lacks PointerEvent; back it with MouseEvent so clientX/clientY survive.
+if (typeof PointerEvent === 'undefined') {
+    class PointerEventPolyfill extends MouseEvent {
+        pointerId: number;
+        constructor(type: string, params: PointerEventInit = {}) {
+            super(type, params);
+            this.pointerId = params.pointerId ?? 1;
+        }
+    }
+    // @ts-expect-error assigning polyfill to the global scope
+    global.PointerEvent = PointerEventPolyfill;
+}
+
+// jsdom lacks pointer capture
+HTMLElement.prototype.setPointerCapture = vi.fn();
+HTMLElement.prototype.releasePointerCapture = vi.fn();