fix(insights): BP chart Y-axis unit reads 'mmHg' not 'Hg'

The blood-pressure chart cards on /insights/blutdruck and on the
mother-page trends row passed `yAxisUnit="Hg"` to the underlying
HealthChart, which painted gridline labels as `139 Hg`. mmHg is the
canonical clinical unit; "Hg" alone is incomplete (mercury, not
millimeters of mercury) and reads as a typo. Tile header on the same
page already says mmHg, so the axis was the only surface drifting.

Per .planning/round-v1433-audit-runtime.md F6.

src/app/insights/blutdruck/page.tsx

@@ -105,7 +105,7 @@ export default function InsightsBlutdruckPage() {
         title={t("charts.bloodPressure")}
         colors={["#ff79c6", "#8be9fd"]}
         unit="mmHg"
-        yAxisUnit="Hg"
+        yAxisUnit="mmHg"
         targetZones={bpTargetZones}
         compareBaseline={compareBaseline}
         userTimezone={user?.timezone}

src/components/insights/trends-row.tsx

@@ -123,7 +123,7 @@ export function TrendsRow({ annotations, confidence }: TrendsRowProps) {
               title={t("charts.bloodPressure")}
               colors={["#ff79c6", "#8be9fd"]}
               unit="mmHg"
-              yAxisUnit="Hg"
+              yAxisUnit="mmHg"
               mini
               userTimezone={userTimezone}
             />