fix(db): stabilize connection settings and explicitly define AppConfig table name

- Set SQL connection idle limit to 1 to reduce resource usage
- Explicitly define AppConfig table name to prevent GORM pluralization issues

internal/db/queries.go

@@ -0,0 +1,11 @@
+package db
+
+import "gorm.io/gorm"
+
+func GetConfig(db *gorm.DB) (*AppConfig, error) {
+	var appConfig AppConfig
+	if err := db.First(&appConfig).Error; err != nil {
+		return nil, err
+	}
+	return &appConfig, nil
+}