feat(design): atmosphere + WhyUs editorial 3-AM treatment

TopographicBg now actually reads:
- Per-line stroke width varies (triangle wave — contour-interval feel)
- Per-line opacity varies by vertical depth (darker mid-section, lighter
  edges)
- One line in four rendered in cyan (echo of cross-route correlation)
- Radial-mask soft edge fade so lines dissolve into the section boundary
- Default opacity bumped from 0.12 to 0.35; section callers still scale it
  down via the opacity prop, but the new internal variation makes the
  atmosphere visible where before it was invisible

WhyUs second tile: 3-AM storytelling moment now lands typographically:
- Decorative 03:00 glyph (amber/4% alpha) in the top-right corner
- Eyebrow log-entry treatment: pulsing amber dot + mono 03:00:47.218
  timestamp + OPS DESK label — reads like a product UI log row
- The rest of the tile unchanged

ProductShowcase figure: figcaption moved to last child (HTML spec
requires figcaption to be first or last in a figure; a div after it was
a validation error).

src/components/sections/ProductShowcase.astro

@@ -48,8 +48,8 @@ const callouts: Callout[] = [
           />
           <div class="absolute inset-0 ring-1 ring-inset ring-accent/10 pointer-events-none rounded-lg"></div>
         </div>
-        <figcaption class="sr-only">Screenshot of a failed exchange in Cameleer, showing the full execution graph, fallback path, and exception context.</figcaption>
         <div aria-hidden="true" class="showcase-shot-glow"></div>
+        <figcaption class="sr-only">Screenshot of a failed exchange in Cameleer, showing the full execution graph, fallback path, and exception context.</figcaption>
       </figure>
 
       <ul class="lg:col-span-4 space-y-7 lg:pt-4">