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/model/models.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"gorm.io/datatypes"
+	"gorm.io/gorm"
 )
 
 type User struct {
@@ -160,8 +161,12 @@ type ModelConfig struct {
 	// successful generation. Independent of the event_log (which is subject to
 	// retention / manual clearing), so the admin "次数" is a true running total.
 	GenerationCount int64 `gorm:"not null;default:0"`
-	CreatedAt       time.Time
-	UpdatedAt       time.Time
+	// DeletedAt soft-deletes the row (vivid parity): hidden from every normal
+	// path, but the row + its counters survive so a re-import revives it
+	// without losing generation_count or pricing.
+	DeletedAt gorm.DeletedAt `gorm:"index"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
 }
 
 func (m ModelConfig) EffectiveName() string {