fix(home): remove <a> wrapper around bento-tile (was breaking grid)

The home service section had each bento-tile wrapped in an
<a href="/services/..."> tag. This caused two problems:

1. The <a> became the grid item instead of the .bento-tile,
   so the .bento-tile's grid-column: span 3 was ignored.
   The <a> defaulted to display: block and stretched to
   100% width, so all 4 tiles in a row had the same wide
   width — but the grid was no longer dividing them equally.

2. Astro's scoped CSS only applies to elements with the
   matching data-astro-cid attribute. The <a> wrapper had
   its own scope, and the .bento-grid > a selector wasn't
   styled — so the grid layout didn't propagate correctly.

Fix: remove the <a> wrapper. Make the whole tile clickable
by adding an absolutely-positioned <a class="tile-link-overlay">
inside the tile (covers the entire tile, sits behind text via
z-index). The .bento-tile is now a direct child of .bento-grid
and grid-column: span 3 works as expected.

Result: 4 tiles width 3/12 each, exactly filling one row,
clickable from anywhere on the tile.

Co-Authored-By: Claude <noreply@anthropic.com>

src/pages/index.astro

@@ -148,16 +148,16 @@ const featuredPortfolio = portfolio.filter(p => p.data.featured).slice(0, 4);
           const span = 3;
           const surface = (['yellow', 'purple-soft', 'mint', 'soft'] as const)[i];
           return (
-            <a href={`/services/${s.id}`} style="display: block; text-decoration: none; color: inherit;">
-              <BentoTile span={span} surface={surface} eyebrow={s.data.badge} title={s.data.title}>
-                <p class="mega-subtitle">{s.data.subtitle}</p>
-                <div class="mega-objective">
-                  <span class="objective-label">เป้าหมาย:</span>
-                  <span class="objective-value">{s.data.objective}</span>
-                </div>
+            <BentoTile span={span} surface={surface} eyebrow={s.data.badge} title={s.data.title}>
+              <p class="mega-subtitle">{s.data.subtitle}</p>
+              <div class="mega-objective">
+                <span class="objective-label">เป้าหมาย:</span>
+                <span class="objective-value">{s.data.objective}</span>
+              </div>
+              <a href={`/services/${s.id}`} class="tile-link-overlay">
                 <span class="mega-cta">ดูรายละเอียด →</span>
-              </BentoTile>
-            </a>
+              </a>
+            </BentoTile>
           );
         })}
       </BentoGrid>