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

frontend/components/admin/AdminSidebar.tsx

@@ -20,11 +20,13 @@ import {
   ImageIcon,
   HelpCircle,
   MessageSquare,
+  Building2,
 } from "lucide-react";
 
 const navItems = [
   { href: "/admin/overview", label: "Overview", icon: LayoutDashboard, adminOnly: false },
   { href: "/admin/events", label: "Events", icon: Calendar, adminOnly: false },
+  { href: "/admin/organizers", label: "Organizers", icon: Building2, adminOnly: false },
   { href: "/admin/gallery", label: "Gallery", icon: ImageIcon, adminOnly: false },
   { href: "/admin/blog", label: "Blog", icon: FileText, adminOnly: false },
   { href: "/admin/faq", label: "FAQ", icon: HelpCircle, adminOnly: false },