fix(schema): enable $ref resolution for directory charts

Set ChartDir only for directory-based charts to enable $ref resolution in
JSON schemas. Archived charts (.tgz) are loaded into memory without filesystem
extraction, so $ref resolution is not supported for them.

This fixes the original issue where `helm template .` and `helm install .`
failed to validate schemas with relative $ref references.

Fixes #31260

Signed-off-by: Benoit Tigeot <benoit.tigeot@lifen.fr>

pkg/chart/common/util/jsonschema.go

@@ -84,6 +84,9 @@ func ValidateAgainstSchemaWithPath(ch chart.Charter, values map[string]any, char
 		return err
 	}
 
+	// Convert chartDir to absolute path for $ref resolution.
+	// If chartDir is empty (e.g., chart loaded from .tgz archive), absChartPath
+	// remains empty and a synthetic path will be used instead.
 	var absChartPath string
 	if chartDir != "" {
 		var err error