add model identities and restore httpx router

backend/internal/models/ai_session.go

@@ -3,13 +3,16 @@ package models
 import "time"
 
 type SenlinAgentAISession struct {
-	ID        uint   `gorm:"primaryKey"`
-	ProjectID uint   `gorm:"index;not null"`
-	CreatedBy uint   `gorm:"index;not null"`
-	Title     string `gorm:"not null"`
-	Context   string `gorm:"type:text"`
-	CreatedAt time.Time
-	UpdatedAt time.Time
+	ID                uint   `gorm:"primaryKey"`
+	Identity          string `gorm:"type:char(36);uniqueIndex"`
+	ProjectID         uint   `gorm:"index;not null"`
+	ProjectIdentity   string `gorm:"type:char(36);index"`
+	CreatedBy         uint   `gorm:"index;not null"`
+	CreatedByIdentity string `gorm:"type:char(36);index"`
+	Title             string `gorm:"not null"`
+	Context           string `gorm:"type:text"`
+	CreatedAt         time.Time
+	UpdatedAt         time.Time
 }
 
 func (SenlinAgentAISession) TableName() string {