Fix hero animation: object-fit cover + conditional blur + glass on collapse

- HeroBackground.vue:
  - Add object-cover class to Lottie animation (fills container)
  - Make dark overlay conditional (v-if collapseProgress > 0.5)
  - Overlay fades in during collapse (opacity 0→1)

- MainNavigation.vue:
  - Replace glassStyle prop with isCollapsed
  - Glass effect (backdrop-blur-md) applies only when collapsed

- topnav.vue:
  - Pass isCollapsed instead of glass-style
  - Home page: isCollapsed from useHeroScroll
  - Other pages: always true (always collapsed)

Result:
- Animation covers full viewport without crop
- No blur overlay when hero is expanded
- Glass effect appears only when header collapses to 100px

app/layouts/topnav.vue

@@ -28,7 +28,7 @@
         :can-search="canSearch"
         :show-mode-toggle="true"
         :show-active-mode="isCatalogSection"
-        :glass-style="isHomePage || isCatalogSection"
+        :is-collapsed="isHomePage ? heroIsCollapsed : true"
         @toggle-theme="toggleTheme"
         @set-catalog-mode="setCatalogMode"
         @sign-out="onClickSignOut"