fix(csvimport): report accurate physical line numbers via FieldPos; add blank-line + zero-row tests

internal/csvimport/csvimport_test.go

@@ -32,3 +32,20 @@ func TestParseRejectsEmptyField(t *testing.T) {
 		t.Fatal("empty password must error")
 	}
 }
+
+func TestParseBlankLineKeepsCorrectLineNumber(t *testing.T) {
+	// blank physical line 2, malformed row on physical line 3
+	_, err := Parse(strings.NewReader("a@x,p1,a@y,p2\n\nbad,row,here\n"))
+	if err == nil {
+		t.Fatal("expected error for 3-column row")
+	}
+	if !strings.Contains(err.Error(), "line 3") {
+		t.Fatalf("error must reference physical line 3, got: %v", err)
+	}
+}
+
+func TestParseZeroRowsErrors(t *testing.T) {
+	if _, err := Parse(strings.NewReader("\n\n   \n")); err == nil {
+		t.Fatal("expected error when no rows parsed")
+	}
+}