fix(uplotV2): tooltip list clips last row and over-scrolls

The Virtuoso scroller height was set to min(totalListHeight, 300), but the
scroll viewport adds 8px top + 8px bottom padding that totalListHeight does
not account for. The box was therefore ~16px shorter than its content,
clipping the last row and showing a scrollbar even when every row would fit.

Add the viewport's vertical padding back into the computed height so it only
scrolls once content genuinely exceeds the max height.

frontend/src/lib/uPlotV2/components/Tooltip/__tests__/Tooltip.test.tsx

@@ -177,7 +177,8 @@ describe('Tooltip', () => {
 		renderTooltip({ uPlotInstance, content });
 
 		const list = screen.getByTestId('uplot-tooltip-list');
-		expect(list).toHaveStyle({ height: '200px' });
+		// Measured height (200) + the scroll viewport's vertical padding (16)
+		expect(list).toHaveStyle({ height: '216px' });
 	});
 
 	it('sets tooltip list height based on content length when Virtuoso reports 0 height', () => {
@@ -188,8 +189,8 @@ describe('Tooltip', () => {
 		renderTooltip({ uPlotInstance, content });
 
 		const list = screen.getByTestId('uplot-tooltip-list');
-		// Falls back to content length: 2 items * 38px = 76px
-		expect(list).toHaveStyle({ height: '76px' });
+		// Falls back to content length (2 * 38 = 76) + vertical padding (16) = 92px
+		expect(list).toHaveStyle({ height: '92px' });
 	});
 });
 

frontend/src/lib/uPlotV2/components/Tooltip/components/TooltipList/TooltipList.tsx

@@ -13,6 +13,11 @@ import Styles from './TooltipList.module.scss';
 // Fallback per-item height before Virtuoso reports the real total.
 const TOOLTIP_ITEM_HEIGHT = 38;
 const LIST_MAX_HEIGHT = 300;
+// Vertical padding (spacing-4 top + bottom) the SCSS applies to the scroll
+// viewport. Virtuoso's reported height covers only the items, so it must be
+// added back — otherwise the box is short by this amount, clipping the last
+// row and showing a scrollbar even when every row would fit.
+const LIST_VERTICAL_PADDING = 16;
 
 interface TooltipListProps {
 	id: string;
@@ -30,13 +35,13 @@ export default function TooltipList({
 	// Use the measured height from Virtuoso when available; fall back to a
 	// per-item estimate on first render. Math.ceil prevents a 1 px
 	// subpixel rounding gap from triggering a spurious scrollbar.
-	const height = useMemo(
-		() =>
-			totalListHeight > 0
-				? Math.ceil(Math.min(totalListHeight, LIST_MAX_HEIGHT))
-				: Math.min(content.length * TOOLTIP_ITEM_HEIGHT, LIST_MAX_HEIGHT),
-		[totalListHeight, content.length],
-	);
+	const height = useMemo(() => {
+		const contentHeight =
+			totalListHeight > 0 ? totalListHeight : content.length * TOOLTIP_ITEM_HEIGHT;
+		return Math.ceil(
+			Math.min(contentHeight + LIST_VERTICAL_PADDING, LIST_MAX_HEIGHT),
+		);
+	}, [totalListHeight, content.length]);
 
 	const handleScroll = useCallback(() => {
 		if (!isScrollEventTriggered.current) {