Add recipient email and milestone notifications on transfer create.

Recipients can be emailed the download link immediately and at optional
reminders (7/3/1 days before unavailable, or when grace period starts).

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/2026_06_09_140000_add_recipient_email_to_transfers.php

@@ -0,0 +1,24 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('transfers', function (Blueprint $table) {
+            $table->string('recipient_email')->nullable()->after('message');
+            $table->json('recipient_email_milestones')->nullable()->after('recipient_email');
+            $table->json('recipient_milestones_sent')->nullable()->after('recipient_email_milestones');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('transfers', function (Blueprint $table) {
+            $table->dropColumn(['recipient_email', 'recipient_email_milestones', 'recipient_milestones_sent']);
+        });
+    }
+};