feat(marketing): replace mock hero with live editor screenshot

Captures /examples/traffic-light → /editor in headless Chromium and saves
the rendered editor as a 3840x2160 (2x DPI) PNG + WebP for the landing
page hero.

The shot includes the code editor on the left (Traffic Light Simulator
.ino), the Arduino Uno on the canvas with three LEDs wired up, the SPICE
nets indicator, and the full chrome — a much stronger first impression
than the previous CSS-mocked schematic.

Generation script lives in the private velxio-prod repo
(scripts/capture-hero.mjs) and can be re-run any time to refresh the
asset against the live deployment.

- /marketing/hero-editor.png (320 KB)
- /marketing/hero-editor.webp (160 KB)
- LandingPage hero <picture> now points at these (loading=eager,
  fetchPriority=high since it's above the fold).

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

frontend/src/pages/LandingPage.tsx

@@ -845,12 +845,14 @@ export const LandingPage: React.FC = () => {
         </div>
         <div className="hero-right">
           <picture>
-            <source srcSet="/image.webp" type="image/webp" />
+            <source srcSet="/marketing/hero-editor.webp" type="image/webp" />
+            <source srcSet="/marketing/hero-editor.png" type="image/png" />
             <img
-              src="/image.png"
-              alt="Velxio simulator preview"
+              src="/marketing/hero-editor.png"
+              alt="Velxio editor with Arduino Uno traffic-light circuit"
               className="hero-preview-img"
-              loading="lazy"
+              loading="eager"
+              fetchPriority="high"
             />
           </picture>
         </div>