refactor: use dependency injection in backend

backend/internal/model/app_config.go

@@ -0,0 +1,20 @@
+package model
+
+type AppConfigVariable struct {
+	Key        string `gorm:"primaryKey;not null" json:"key"`
+	Type       string `json:"type"`
+	IsPublic   bool   `json:"-"`
+	IsInternal bool   `json:"-"`
+	Value      string `json:"value"`
+}
+
+type AppConfig struct {
+	AppName             AppConfigVariable
+	BackgroundImageType AppConfigVariable
+	LogoImageType       AppConfigVariable
+	SessionDuration     AppConfigVariable
+}
+
+type AppConfigUpdateDto struct {
+	AppName string `json:"appName" binding:"required"`
+}