feat: add In-Reply-To option (#165)

apps/web/prisma/migrations/20250523232535_add_in_reply_to/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "Email" ADD COLUMN     "inReplyToId" TEXT;

apps/web/prisma/schema.prisma

@@ -245,6 +245,7 @@ model Email {
   attachments  String?
   campaignId   String?
   contactId    String?
+  inReplyToId  String?
   team         Team         @relation(fields: [teamId], references: [id], onDelete: Cascade)
   emailEvents  EmailEvent[]