a11y(insights): hide the workouts back-link arrow from assistive tech

The workouts detail back-link's `ArrowLeft` glyph carried no
`aria-hidden`, so a screen reader announced it alongside the link text. Add
`aria-hidden="true"`, matching the sibling values detail page's back-link.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit 108c3ff583a707b100570e2999b129055f90c76f)

src/app/insights/workouts/[id]/page.tsx

@@ -49,7 +49,7 @@ export default function InsightsWorkoutDetailPage({
           className="-ml-2 w-fit"
         >
           <Link href="/insights/workouts">
-            <ArrowLeft className="mr-1 size-4" />
+            <ArrowLeft className="mr-1 size-4" aria-hidden="true" />
             {t("insights.workouts.detail.backToList")}
           </Link>
         </Button>