fix(i18n): trend-card comparison aria-label uses translation key (H3)

The compareDelta `aria-label` interpolated `"vs. last month"` and
`"vs. last year"` as literal English strings regardless of locale.
A DE user got an English screen-reader announcement next to a
visible German caption ("Δ −2.3 kg vs. Vormonat"). Routed through
`t("comparison.captionLastMonth" | "comparison.captionLastYear")`
so screen-reader output matches the visible text in both locales.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/charts/trend-card.tsx

@@ -226,11 +226,11 @@ export function TrendCard({
             )}
             data-slot="tile-compare-delta"
             data-compare-baseline={compareBaseline}
-            aria-label={`${formatDelta(compareDelta)}${unit ? ` ${unit}` : ""} ${
+            aria-label={`${formatDelta(compareDelta)}${unit ? ` ${unit}` : ""} ${t(
               compareBaseline === "lastMonth"
-                ? "vs. last month"
-                : "vs. last year"
-            }`}
+                ? "comparison.captionLastMonth"
+                : "comparison.captionLastYear",
+            )}`}
           >
             {`Δ ${formatDelta(compareDelta)}${unit ? ` ${unit}` : ""} ${t(
               compareBaseline === "lastMonth"