feat: schema for visa tracking (additive)

Adds VisaStatus enum, VisaApplication model 1:1 with AttendingMember
(cascade-delete), and Program.visaStatusVisibleToMembers Boolean
toggle. The model intentionally stores process metadata only — status,
optional nationality, key dates, free-text notes. Sensitive documents
(passport scans, invitation letters, decision papers) continue to flow
over email and are never persisted in the platform.

Migration is purely additive: CREATE TYPE / CREATE TABLE / ADD COLUMN /
ADD FK. No DROP / ALTER on existing data.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prisma/migrations/20260428172835_add_visa_tracking/migration.sql

@@ -0,0 +1,30 @@
+-- CreateEnum
+CREATE TYPE "VisaStatus" AS ENUM ('NOT_NEEDED', 'REQUESTED', 'INVITATION_SENT', 'APPOINTMENT_BOOKED', 'GRANTED', 'DENIED');
+
+-- AlterTable
+ALTER TABLE "Program" ADD COLUMN     "visaStatusVisibleToMembers" BOOLEAN NOT NULL DEFAULT true;
+
+-- CreateTable
+CREATE TABLE "VisaApplication" (
+    "id" TEXT NOT NULL,
+    "attendingMemberId" TEXT NOT NULL,
+    "status" "VisaStatus" NOT NULL DEFAULT 'REQUESTED',
+    "nationality" TEXT,
+    "invitationSentAt" TIMESTAMP(3),
+    "appointmentAt" TIMESTAMP(3),
+    "decisionAt" TIMESTAMP(3),
+    "notes" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "VisaApplication_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "VisaApplication_attendingMemberId_key" ON "VisaApplication"("attendingMemberId");
+
+-- CreateIndex
+CREATE INDEX "VisaApplication_status_idx" ON "VisaApplication"("status");
+
+-- AddForeignKey
+ALTER TABLE "VisaApplication" ADD CONSTRAINT "VisaApplication_attendingMemberId_fkey" FOREIGN KEY ("attendingMemberId") REFERENCES "AttendingMember"("id") ON DELETE CASCADE ON UPDATE CASCADE;