feat: add linear booking workflow — Новая → Связались → Подтверждено/Отказ

- Add status + confirmed_date columns to group_bookings (migration #10)
- Linear flow: Новая shows "Связались →", Связались shows date picker + "Отказ"
- Date picker for confirmation allows only today and future dates
- Confirmed bookings show the scheduled date
- Filter chips: Все / Новая / Связались / Подтверждено / Отказ with counts
- Declined bookings sorted to bottom of list
- "Сбросить" button on confirmed/declined to restart flow

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

src/app/api/admin/group-bookings/route.ts

@@ -1,5 +1,6 @@
 import { NextRequest, NextResponse } from "next/server";
-import { getGroupBookings, toggleGroupBookingNotification, deleteGroupBooking } from "@/lib/db";
+import { getGroupBookings, toggleGroupBookingNotification, deleteGroupBooking, setGroupBookingStatus } from "@/lib/db";
+import type { BookingStatus } from "@/lib/db";
 
 export async function GET() {
   const bookings = getGroupBookings();
@@ -22,6 +23,15 @@ export async function PUT(request: NextRequest) {
       toggleGroupBookingNotification(id, field, value);
       return NextResponse.json({ ok: true });
     }
+    if (body.action === "set-status") {
+      const { id, status, confirmedDate } = body;
+      const valid: BookingStatus[] = ["new", "contacted", "confirmed", "declined"];
+      if (!id || !valid.includes(status)) {
+        return NextResponse.json({ error: "id and valid status are required" }, { status: 400 });
+      }
+      setGroupBookingStatus(id, status, confirmedDate);
+      return NextResponse.json({ ok: true });
+    }
     return NextResponse.json({ error: "Unknown action" }, { status: 400 });
   } catch (err) {
     console.error("[admin/group-bookings] error:", err);