feat(writers): quote default values based on SQL column type

Bun and GORM struct tags now emit quoted defaults for string/date/time/UUID
columns (e.g. default:'disconnected') and unquoted defaults for numeric and
boolean columns (e.g. default:0, default:true). Function-call expressions
such as now() or gen_random_uuid() are never quoted regardless of type.

Adds QuoteDefaultValue(value, sqlType) helper in pkg/writers and updates
both type mappers and the bun writer tests accordingly.

pkg/writers/gorm/type_mapper.go

@@ -238,8 +238,8 @@ func (tm *TypeMapper) BuildGormTag(column *models.Column, table *models.Table) s
 
 	// Default value
 	if column.Default != nil {
-		// Sanitize default value to remove backticks
-		safeDefault := writers.SanitizeStructTagValue(fmt.Sprintf("%v", column.Default))
+		// Sanitize default value to remove backticks, then quote based on column type
+		safeDefault := writers.QuoteDefaultValue(writers.SanitizeStructTagValue(fmt.Sprintf("%v", column.Default)), column.Type)
 		parts = append(parts, fmt.Sprintf("default:%s", safeDefault))
 	}