navbar: collapse to mobile menu at 1100 px (was 768 px)

Bumps the desktop/mobile split from Tailwind's md (768 px) to a
custom min-[1100px] threshold so tablets and small laptops get the
mobile chrome (menu button + bottom-right floating cluster) instead
of an over-cramped desktop nav. Bottom-clearance spacers on Home and
Shop track the same threshold so they don't disappear before the
floating cluster does.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/ShopPage.vue

@@ -254,10 +254,11 @@ onBeforeUnmount(() => {
   <Footer />
 
   <!-- Bottom clearance for the mobile floating cluster (search / cart /
-       menu), same pattern as HomePage so both pages align visually. -->
+       menu), same pattern as HomePage so both pages align visually.
+       Tied to the navbar's 1100 px collapse threshold. -->
   <div
     aria-hidden="true"
-    class="md:hidden"
+    class="min-[1100px]:hidden"
     style="height: calc(100px + env(safe-area-inset-bottom));"
   />