fix: update avatar dimensions in hero section (Tier 1) to match CSS

The previous commit fixed the Tier 2 default hero avatar (home.njk),
but production uses the homepage builder (Tier 1) which renders
hero.njk instead. Same issue: HTML width/height 96x96 but CSS sets
sm:w-32/h-32 (128px) on desktop, causing CLS on resize.

Confab-Link: http://localhost:8080/sessions/edb1b7b0-da66-4486-bd9c-d1cfa7553b88

_includes/components/sections/hero.njk

@@ -19,8 +19,8 @@
     <img
       src="{{ authorAvatar }}"
       alt="{{ authorName }}"
-      width="96"
-      height="96"
+      width="128"
+      height="128"
       class="w-24 h-24 sm:w-32 sm:h-32 rounded-full object-cover shadow-lg flex-shrink-0"
       loading="eager"
     >