feat(models): 对齐 vivid 新改动——模型删除改软删,重导不丢计数/定价

- model_configs 加 deleted_at(gorm 软删),List/Get 自动过滤,
  GetAny/Unscoped 用于复活与孤儿清理路径
- 渠道同步/删渠道/管理端删除模型的孤儿清理全部走软删
- 导入时若命中软删行:UpdateAny + deleted_at=NULL 复活,
  generation_count 与原定价保留(vivid a42f32c 同语义)
- provider 时代残留仍物理删除(DeleteHard),不留软删垃圾
- OrphanModelIDs 跳过已软删行,避免重复清扫
- btn-primary 禁用态改浅灰填充(vivid d636105)

核对过已等价的:vivid 僵尸任务兜底(我们的 ResumeStaleJob+
PurgeStale+MarkRefunded 同语义)、产物 MIME 魔数嗅探、
retention 按创建时间、渠道同步弹窗(开关+别名)均已覆盖。

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

backend/internal/repo/channel_repo.go

@@ -212,13 +212,14 @@ func (r *ChannelRepository) ChannelIDsByModel(ctx context.Context, modelID strin
 }
 
 // OrphanModelIDs returns local model ids that no channel binds anymore.
+// Soft-deleted rows are skipped — they're already gone from every live path.
 func (r *ChannelRepository) OrphanModelIDs(ctx context.Context) ([]string, error) {
 	var ids []string
 	err := r.db.WithContext(ctx).
 		Table("model_configs").
 		Select("model_configs.id").
 		Joins("LEFT JOIN channel_models ON channel_models.model_id = model_configs.id").
-		Where("channel_models.model_id IS NULL").
+		Where("channel_models.model_id IS NULL AND model_configs.deleted_at IS NULL").
 		Scan(&ids).Error
 	return ids, err
 }