fix(release): 发布检查 - 修复 v1.6.1 后端测试失败

兑换码购买链接默认改为空，避免非法占位文案导致外观保存失败；迁移清单补上 upload_reservations；按首尾帧后的实测体积上调 Agent 工具 schema 预算；Grok 生图测试覆盖 response_format 开关的两种返回。

backend/cmd/migrate-sqlite-postgres/main.go

@@ -408,6 +408,7 @@ func migrations() []tableMigration {
 		migrateTable[model.UserOSSSetting]("user_oss_settings"),
 		migrateTable[model.StorageLocation]("storage_locations"),
 		migrateTable[model.UserDailyUploadUsage]("user_daily_upload_usages"),
+		migrateTable[model.UploadReservation]("upload_reservations"),
 		migrateTable[model.Skill]("skills"),
 		migrateTable[model.SkillLibraryCategory]("skill_library_categories"),
 		migrateTable[model.SkillVersion]("skill_versions"),