fix(hero): fix mosaic layout full-width + update screenshots

- Override inherited 2-column grid from .hero by adding display: block to .hero--mosaic
- Add explicit grid-column/grid-row for mosaic cells 3 & 4 to prevent auto-placement issues
- Slice heroData to 4 images to match 4 defined grid cells
- Regenerate hero-mosaic-home.png and theme-studio-home.png screenshots

app/page.tsx

@@ -145,7 +145,7 @@ export default async function HomePage() {
     return (
       <div className="hero hero--mosaic">
         <div className="hero__mosaic-grid">
-          {heroData.slice(0, 6).map((img, i) => (
+          {heroData.slice(0, 4).map((img, i) => (
             <div key={i} className={`hero__mosaic-cell hero__mosaic-cell--${i + 1}`}>
               <Image
                 src={img.src}