feat: logistics page shell + Confirmations/Travel/Hotels tabs

- /admin/logistics page with shadcn Tabs (3 active + 5 disabled "(soon)"
  placeholder tabs for Visas / Lunch / Documents / Email Templates / Settings).
- Sidebar entry "Logistics" between Mentors and Awards (Plane icon).
- Confirmations tab: read-only table with status filter pills, browser-
  local-time deadline display, attendee count, decline reason snippet.
- Hotels tab: single-hotel form (name/address/link/notes) with live
  email-preview card showing what teams will see.
- Travel tab: per-attendee flight tracker with arrival/departure
  datetimes, flight numbers, IATA airports, click-to-toggle status badge,
  edit Sheet, and unfilled/pending/confirmed filter pills.

Smoke-tested end-to-end: navigation, sidebar entry, all three tabs
render, hotel save persists to DB and renders in preview card.

src/components/layouts/admin-sidebar.tsx

@@ -33,6 +33,7 @@ import {
   GraduationCap,
   Handshake,
   History,
+  Plane,
   Trophy,
   User,
   MessageSquare,
@@ -91,6 +92,11 @@ const navigation: NavItem[] = [
     href: '/admin/mentors',
     icon: GraduationCap,
   },
+  {
+    name: 'Logistics',
+    href: '/admin/logistics',
+    icon: Plane,
+  },
   {
     name: 'Awards',
     href: '/admin/awards',