Allow multiple hosting servers per sold version.

Drop unique tenant_id on server_accounts and add create/update/delete/renew APIs per server account, with list/expiring using the worst status.

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

prisma/schema.prisma

@@ -71,7 +71,8 @@ model Tenant {
   updatedAt        DateTime    @updatedAt @map("updated_at")
   auditLogs        AuditLog[]
   smsAccount       SmsAccount?
-  serverAccount    ServerAccount?
+  /// 0..N hosting/billing servers per sold version (not the same as nodeServer API URL)
+  serverAccounts   ServerAccount[]
   pluginSubscriptions PluginSubscription[]
 
   @@index([product])
@@ -187,7 +188,7 @@ model AuditLog {
 /// isDedicated=false → we manage charge/renewal/expiry alerts.
 model ServerAccount {
   id               String    @id @default(cuid())
-  tenantId         String    @unique @map("tenant_id")
+  tenantId         String    @map("tenant_id")
   isDedicated      Boolean   @default(false) @map("is_dedicated")
   serverName       String?   @map("server_name")
   specs            String?
@@ -209,6 +210,7 @@ model ServerAccount {
   tenant  Tenant         @relation(fields: [tenantId], references: [id], onDelete: Cascade)
   charges ServerCharge[]
 
+  @@index([tenantId])
   @@index([expiresAt])
   @@index([isDedicated])
   @@map("server_accounts")