feat: improve prompt management (#7853)

packages/backend/server/schema.prisma

@@ -367,6 +367,9 @@ model AiPrompt {
   model     String   @db.VarChar
   config    Json?    @db.Json
   createdAt DateTime @default(now()) @map("created_at") @db.Timestamptz(3)
+  updatedAt DateTime @default(now()) @map("updated_at") @db.Timestamptz(3)
+  // whether the prompt is modified by the admin panel
+  modified  Boolean  @default(false)
 
   messages AiPromptMessage[]
   sessions AiSession[]