Show whole-number metrics as whole numbers

The dashboard tiles printed every value at one decimal: '121,0 mmHg',
'60,0 bpm', '9.240,0' steps. TrendCard takes the metric's precision, and
blood pressure, pulse, HRV, steps and mg/dL glucose pass zero. The
measurement list names count-shaped units the way the insights pages do
('13 Etagen', '12,5 Atemzüge/min') instead of the source's 'count'.

src/components/charts/__tests__/trend-card-fraction-digits.test.tsx

@@ -0,0 +1,52 @@
+import { describe, it, expect } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+import { Activity } from "lucide-react";
+
+import { TrendCard } from "../trend-card";
+import { I18nProvider } from "@/lib/i18n/context";
+
+/**
+ * A whole-number metric reads as a whole number on the tile: "121 mmHg",
+ * not "121,0 mmHg", and "9.240" steps rather than "9.240,0".
+ */
+function render(node: React.ReactNode) {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale="de">{node}</I18nProvider>,
+  );
+}
+
+const base = {
+  label: "Schritte",
+  latest: 9240,
+  unit: "",
+  avg7: 9535.14,
+  avg30: 9100,
+  slope30: null,
+  icon: Activity,
+};
+
+describe("<TrendCard> fractionDigits", () => {
+  it("keeps one decimal by default", () => {
+    const html = render(<TrendCard {...base} />);
+    expect(html).toContain("9.240,0");
+  });
+
+  it("prints whole numbers, averages and deltas at 0", () => {
+    const html = render(
+      <TrendCard {...base} fractionDigits={0} trend7Delta={-1383.2} />,
+    );
+    expect(html).toContain("9.240");
+    expect(html).not.toContain("9.240,0");
+    expect(html).toContain("9.535");
+    expect(html).not.toContain("9.535,1");
+    expect(html).toContain("−1.383");
+    expect(html).not.toContain("−1.383,2");
+  });
+
+  it("reads a sub-step delta as zero at 0 decimals", () => {
+    const html = render(
+      <TrendCard {...base} fractionDigits={0} trend7Delta={0.3} />,
+    );
+    expect(html).toContain("±0");
+  });
+});

src/components/charts/trend-card.tsx

@@ -101,6 +101,13 @@ interface TrendCardProps {
    * before (no reserved space, no layout shift).
    */
   valueAdornment?: React.ReactNode;
+  /**
+   * Decimal places for the headline, the averages and the deltas. Defaults
+   * to 1. A whole-number metric (steps, mmHg, bpm, mg/dL) passes 0 so the
+   * tile reads "121 mmHg", not "121,0 mmHg" — the precision its own
+   * insights page uses.
+   */
+  fractionDigits?: number;
 }
 
 export function TrendCard({
@@ -123,6 +130,7 @@ export function TrendCard({
   staleDays = null,
   emptyHint = null,
   valueAdornment = null,
+  fractionDigits = 1,
 }: TrendCardProps) {
   const { t, tCount } = useTranslations();
   const fmt = useFormatters();
@@ -152,7 +160,7 @@ export function TrendCard({
   const arrowSentiment = getTrendSentiment(primarySignal, directionSentiment);
   const trendColor = sentimentColorClass(arrowSentiment);
 
-  const formatValue = (value: number) => fmt.number(value, 1);
+  const formatValue = (value: number) => fmt.number(value, fractionDigits);
 
   // v1.4.15 Fix 4 — the 7-day delta now shares the arrow's colour so
   // both elements communicate the same sentiment for the same signal.
@@ -171,9 +179,10 @@ export function TrendCard({
   const comparisonDeltaColor = sentimentColorClass(comparisonSentiment);
 
   const formatDelta = (value: number): string => {
-    if (Math.abs(value) < 0.05) return `±0`;
+    // Below half a step of the shown precision the delta prints as zero.
+    if (Math.abs(value) < 0.5 * 10 ** -fractionDigits) return `±0`;
     const sign = value > 0 ? "+" : "−";
-    return `${sign}${fmt.number(Math.abs(value), 1)}`;
+    return `${sign}${fmt.number(Math.abs(value), fractionDigits)}`;
   };
 
   // The label flips from "7d" / "7T" (mean) to "7d trend" / "7T-Trend"