Add dbgenerated default for displayId

prisma db push cannot add a non-nullable column to an existing table
without a database-level default. Using a PostgreSQL expression to
generate V + 9 random digits as the fallback default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/prisma/schema.prisma

@@ -67,7 +67,7 @@ model Item {
 
 model Ticket {
   id          String       @id @default(cuid())
-  displayId   String       @unique
+  displayId   String       @unique @default(dbgenerated("concat('V', (floor(random() * 900000000) + 100000000)::bigint::text)"))
   title       String
   overview    String
   severity    Int