[management,misc] Fix configuration migration checks

The initial migration let an empty legacy Datadir override Management defaults and pulled Viper into WASM builds through the common util package.

Normalize the Management data directory, isolate template expansion from the loader dependency, and split source binding to satisfy the quality gate.

util/file.go

@@ -12,7 +12,7 @@ import (
 
 	log "github.com/sirupsen/logrus"
 
-	configloader "github.com/netbirdio/netbird/util/config"
+	"github.com/netbirdio/netbird/util/envtemplate"
 )
 
 func WriteBytesWithRestrictedPermission(ctx context.Context, file string, bs []byte) error {
@@ -243,7 +243,7 @@ func ReadJsonWithEnvSub(file string, res interface{}) (interface{}, error) {
 		return nil, err
 	}
 
-	output, err := configloader.ExpandEnvTemplate(bs)
+	output, err := envtemplate.Expand(bs)
 	if err != nil {
 		return nil, err
 	}