refactor: remove obsolete project mode

prisma/migrations/20260324120000_drop_project_mode/migration.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `projects`
+  DROP COLUMN `mode`;

prisma/schema.prisma

@@ -353,7 +353,6 @@ model Project {
   id                 String                 @id @default(uuid())
   name               String
   description        String?                @db.Text
-  mode               String                 @default("novel-promotion")
   userId             String
   createdAt          DateTime               @default(now())
   updatedAt          DateTime               @default(now()) @updatedAt

prisma/schema.sqlit.prisma

@@ -347,7 +347,6 @@ model Project {
   id                 String                 @id @default(uuid())
   name               String
   description        String?
-  mode               String                 @default("novel-promotion")
   userId             String
   createdAt          DateTime               @default(now())
   updatedAt          DateTime               @default(now()) @updatedAt