Fix Homepage collage's active photo effect while hover

- Change method and use a class on collage itself fading all photos, then highlight the one being hovered
- For some reason the content inside was conflicting the mouseenter event

src/components/organisms/Collage.svelte

@@ -7,7 +7,7 @@
 </script>
 
 {#if photos}
-    <div class="collage">
+    <div class="collage" class:is-hovering={hovered !== null}>
         {#each photos as { slug, title, image, location, city }, index}
             <PhotoCard
                 id={image.id}
@@ -16,7 +16,7 @@
                 title={title}
                 location={location}
                 city={city}
-                hovered={hovered !== null && hovered !== index}
+                hovered={hovered === index}
                 on:hover={({ detail }) => hovered = detail ? index : null}
             />
         {/each}