refactor: shorten model and table prefixes

backend/internal/models/user.go

@@ -2,7 +2,7 @@ package models
 
 import "time"
 
-type SenlinAgentUser struct {
+type SaUser struct {
 	ID           uint   `gorm:"primaryKey"`
 	Identity     string `gorm:"type:char(36);uniqueIndex"`
 	Email        string `gorm:"uniqueIndex;not null"`
@@ -13,6 +13,6 @@ type SenlinAgentUser struct {
 	UpdatedAt    time.Time
 }
 
-func (SenlinAgentUser) TableName() string {
-	return "senlin_agent_users"
+func (SaUser) TableName() string {
+	return "sa_users"
 }