fix(launcher): remove wasted top space in iframe/menu-hidden mode; vh bottom buffer

events/+layout.svelte:
  the events nav is actually rendered. Adds pt-0 for the launcher case
  (nav never rendered there; launcher manages its own header offset).
- pb-48 (fixed 12rem) → pb-[25vh] — scrolls ~25% of viewport below
  last card on any screen size, scales properly on phone/tablet/desktop.

launcher/+layout.svelte outer wrapper:
- Static mt-4 replaced with conditional:
    mt-12 when launcher header is visible (matches h-12 header height,
           keeps content clear of the absolute overlay)
    mt-2  when launcher header is hidden (minimal breathing room only)
- Result: iframe mode + launcher_header=hide → near-zero top dead space

src/routes/events/[event_id]/(launcher)/launcher/+layout.svelte

@@ -537,11 +537,13 @@
 </svelte:head>
 
 <div
+    class:mt-12={!$events_loc.launcher.hide__launcher_header}
+    class:mt-2={$events_loc.launcher.hide__launcher_header}
     class="
         static
         m-auto
         border-x border-gray-200 dark:border-gray-600
-        mt-4 mb-16 sm:mb-12
+        mb-16 sm:mb-12
         h-full
         w-full max-w-7xl
         transition-all