feat: allow administrator deletion and remove icon source field

apps/api/prisma/migrations/20261005150000_remove_icon_source/migration.sql

@@ -0,0 +1 @@
+ALTER TABLE `Icon` DROP COLUMN `source`;

apps/api/prisma/schema.prisma

@@ -325,8 +325,6 @@ model Icon {
   hash String @db.Char(64)
   /// 规范化静态 PNG 图片二进制
   data Bytes @db.MediumBlob
-  /// 可选公开来源网址
-  source String? @db.VarChar(500)
   /// 记录创建时间，UTC
   createdAt DateTime @default(now())
   positions Position[]