feat(design): new ProductShowcase section — 'When something breaks'

Editorial section between DualValueProps and HowItWorks. Breaks the
identical-rectangle cascade with an asymmetric 8/4 grid: large
error-detail screenshot with subtle cyan/amber backlight on the left,
three numbered callout captions on the right.

The screenshot (cross-route correlation chain + circuit breaker +
fallback + Java stack trace) makes the 'deep tracing, replay, live
control' claims concrete in a way the abstract RouteDiagram never did.

Cyan kicker on this section (vs. amber elsewhere) signals 'this one is
different' and echoes the cross-route correlation color in the product.

src/pages/index.astro

@@ -4,6 +4,7 @@ import SiteHeader from '../components/SiteHeader.astro';
 import SiteFooter from '../components/SiteFooter.astro';
 import Hero from '../components/sections/Hero.astro';
 import DualValueProps from '../components/sections/DualValueProps.astro';
+import ProductShowcase from '../components/sections/ProductShowcase.astro';
 import HowItWorks from '../components/sections/HowItWorks.astro';
 import WhyUs from '../components/sections/WhyUs.astro';
 import PricingTeaser from '../components/sections/PricingTeaser.astro';
@@ -17,6 +18,7 @@ import FinalCTA from '../components/sections/FinalCTA.astro';
   <main>
     <Hero />
     <DualValueProps />
+    <ProductShowcase />
     <HowItWorks />
     <WhyUs />
     <PricingTeaser />