feat: add status workflow to MC and Open Day bookings, refactor into separate files

- DB migration v12: add status column to mc_registrations and open_day_bookings
- MC and Open Day tabs now have full status workflow (new → contacted → confirmed/declined)
- Filter tabs with counts, status badges, action buttons matching group bookings
- Extract shared components (_shared.tsx): FilterTabs, StatusBadge, StatusActions, BookingCard, ContactLinks
- Split monolith into _McRegistrationsTab.tsx, _OpenDayBookingsTab.tsx, _shared.tsx

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app/api/admin/open-day/bookings/route.ts

@@ -3,6 +3,7 @@ import {
   getOpenDayBookings,
   toggleOpenDayNotification,
   deleteOpenDayBooking,
+  setOpenDayBookingStatus,
 } from "@/lib/db";
 
 export async function GET(request: NextRequest) {
@@ -16,6 +17,15 @@ export async function GET(request: NextRequest) {
 export async function PUT(request: NextRequest) {
   try {
     const body = await request.json();
+    if (body.action === "set-status") {
+      const { id, status } = body;
+      if (!id || !status) return NextResponse.json({ error: "id, status required" }, { status: 400 });
+      if (!["new", "contacted", "confirmed", "declined"].includes(status)) {
+        return NextResponse.json({ error: "Invalid status" }, { status: 400 });
+      }
+      setOpenDayBookingStatus(id, status);
+      return NextResponse.json({ ok: true });
+    }
     if (body.action === "toggle-notify") {
       const { id, field, value } = body;
       if (!id || !field || typeof value !== "boolean") {