fix(insights): align the target reference card to the shared card surface

The per-metric target reference panel rendered on a borderless
`bg-muted/30` inset, which read as a nested detail block rather than a
top-level card. Side-by-side with the assessment, trajectory, trend and
recommendation cards on the same category page it looked off-tone. Match
the compact card surface those siblings use (`bg-card/20` tint, a
`border-border/40` hairline, the shared `rounded-lg`) so the panel reads
as one family.

src/components/insights/metric-target-summary.tsx

@@ -284,7 +284,7 @@ function TargetReferencePanel({
     <div
       data-slot="metric-target-summary"
       data-target-type={target.type}
-      className="bg-muted/30 space-y-3 rounded-lg px-3 py-2.5"
+      className="border-border/40 bg-card/20 space-y-3 rounded-lg border px-3 py-2.5"
     >
       {/* Row 1: target range string + status pill + source link. */}
       <div className="flex flex-wrap items-center justify-between gap-x-4 gap-y-1.5">