Validate Helm source URL schemes

Reject HelmRepository source URLs with schemes unsupported by the
source-controller API before generating or applying the object.

Signed-off-by: Immanuel Tikhonov <pchpr.00@list.ru>
Assisted-by: codex/gpt-5

cmd/flux/create_source_helm_test.go

@@ -36,6 +36,12 @@ func TestCreateSourceHelm(t *testing.T) {
 			resultFile: "name is required",
 			assertFunc: "assertError",
 		},
+		{
+			name:       "unsupported URL scheme",
+			args:       "create source helm podinfo --url=git://example.com/charts --export",
+			resultFile: "url scheme 'git' not supported, can be: http, https and oci",
+			assertFunc: "assertError",
+		},
 		{
 			name:       "OCI repo",
 			args:       "create source helm podinfo --url=oci://ghcr.io/stefanprodan/charts/podinfo --interval 5m --export",