fix some linter issues

Author: csibepapa

src/trackr/cli.py

@@ -261,7 +261,7 @@ def list_cmd(
         typer.echo("No items found.")
         return
 
-    VALID_FIELDS = {# module top-level
+    valid_fields = {# module top-level
         "id",
         "title",
         "description",
@@ -275,7 +275,7 @@ def list_cmd(
         selected_fields = [f.strip() for f in fields.split(",")]
 
         for f in selected_fields:
-            if f not in VALID_FIELDS:
+            if f not in valid_fields:
                 raise typer.BadParameter(f"Invalid field: {f}")
 
     for row in rows: