feat: organizers, meetups UI, Plausible analytics, and migration tooling

- Add organizer model/API, admin and public organizer pages, meetup cards
- Refresh events/home/contact; add calendar dialog and carousel components
- Optional Plausible via NEXT_PUBLIC_PLAUSIBLE_* env vars in root layout
- Prisma migration, seed updates, baseline-and-migrate script

Made-with: Cursor

backend/prisma/seed.ts

@@ -56,6 +56,16 @@ async function main() {
     });
   }
 
+  const defaultOrganizer = await prisma.organizer.upsert({
+    where: { slug: 'belgian-bitcoin-embassy' },
+    update: {},
+    create: {
+      id: '00000000-0000-4000-8000-000000000001',
+      name: 'Belgian Bitcoin Embassy',
+      slug: 'belgian-bitcoin-embassy',
+    },
+  });
+
   const existingMeetup = await prisma.meetup.findFirst({
     where: { title: 'Monthly Bitcoin Meetup' },
   });
@@ -70,8 +80,9 @@ async function main() {
         time: '19:00',
         location: 'Brussels, Belgium',
         link: 'https://meetup.com/example',
-        status: 'UPCOMING',
+        status: 'PUBLISHED',
         featured: true,
+        organizerId: defaultOrganizer.id,
       },
     });
   }