🔧 Fix asset file references for Portal presentation render

- Update DashboardOverviewScene to use einundzwanzig-square-inverted.svg
  instead of non-existent einundzwanzig-logo.png
- Fix MeetupShowcaseScene logo extensions: EinundzwanzigKempten.jpg and
  EinundzwanzigMemmingen.jpg (were incorrectly .png)
- Fix TopMeetupsScene logo extensions: EinundzwanzigKempten.jpg and
  EinundzwanzigTrier.jpg (were incorrectly .png)
- Update corresponding mobile scenes with same fixes
- Update test file expectations to match corrected extensions

These fixes enable successful full render of both PortalPresentation
(1920x1080) and PortalPresentationMobile (1080x1920) compositions.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

videos/src/scenes/portal/mobile/MeetupShowcaseSceneMobile.tsx

@@ -24,7 +24,7 @@ const UPCOMING_MEETUPS = [
     location: "Kempten im Allgäu",
     date: "Di, 28. Jan 2025",
     time: "19:00 Uhr",
-    logoPath: "logos/EinundzwanzigKempten.png",
+    logoPath: "logos/EinundzwanzigKempten.jpg",
     isFeatured: true,
   },
   {
@@ -32,7 +32,7 @@ const UPCOMING_MEETUPS = [
     location: "Memmingen",
     date: "Mi, 29. Jan 2025",
     time: "19:30 Uhr",
-    logoPath: "logos/EinundzwanzigMemmingen.png",
+    logoPath: "logos/EinundzwanzigMemmingen.jpg",
     isFeatured: false,
   },
   {