fix(insights): isolate hero glow from sticky section nav

The hero band's glow-purple box-shadow bled through the sticky
section nav (bg-background/80 + backdrop-blur) so the nav painted
with a faint purple cast on scroll. Add `isolate` to the hero
container so the shadow stays z-trapped inside its own stacking
context.

Fixes Design-HIGH-4.

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

src/components/insights/hero-strip.tsx

@@ -182,7 +182,12 @@ export function HeroStrip({
       data-slot="insights-hero-strip"
       className={cn(
         "hero-gradient glow-purple animate-insight-in",
-        "relative overflow-hidden rounded-xl px-4 py-5 sm:px-6 sm:py-6",
+        // `isolate` creates a new stacking context so the purple glow
+        // box-shadow stays z-trapped inside the hero band — without
+        // it the shadow bled through the sticky section nav below
+        // (the nav uses bg-background/80 + backdrop-blur, which the
+        // shadow leaked through).
+        "relative isolate overflow-hidden rounded-xl px-4 py-5 sm:px-6 sm:py-6",
       )}
     >
       {/*