fix(sub): drop empty remark segments instead of leaving a stray separator

expandSegment dropped a "|" segment only when its tokens rendered the unlimited
mark, so a segment whose only token resolved to the empty string (a client with
no comment, an unlimited client's expiry date) was kept as bare decoration,
leaving a trailing "|" or a dangling emoji on every share link's remark. Drop a
token-bearing segment whenever none of its tokens produce a real value, while
still keeping pure-literal segments.

internal/sub/remark_vars_test.go

@@ -128,6 +128,23 @@ func TestExpandRemarkVars_DropUnlimitedSegments(t *testing.T) {
 	}
 }
 
+func TestExpandRemarkVars_DropEmptySegments(t *testing.T) {
+	inbound := &model.Inbound{Remark: "host"}
+
+	// A client with no comment: the {{COMMENT}} segment resolves to empty and
+	// must be dropped, not left as a trailing "|".
+	noComment := expandCtx(model.Client{}, xray.ClientTraffic{Enable: true}, inbound)
+	if got := expandRemarkVars("{{INBOUND}}|{{COMMENT}}", noComment); got != "host" {
+		t.Errorf("empty comment segment = %q, want %q (no trailing pipe)", got, "host")
+	}
+
+	// A decorated empty segment (emoji + empty token) drops whole, not leaving
+	// a dangling emoji.
+	if got := expandRemarkVars("{{INBOUND}}|📅{{EXPIRE_DATE}}", noComment); got != "host" {
+		t.Errorf("decorated empty segment = %q, want %q", got, "host")
+	}
+}
+
 func TestClientStatus(t *testing.T) {
 	cases := []struct {
 		name string