add custom error class SlobsCliError

add exception group handling for all commands that may raise exceptions

add comments to for-else blocks

src/slobs_cli/errors.py

@@ -0,0 +1,13 @@
+import asyncclick as click
+
+
+class SlobsCliError(click.ClickException):
+    """Base class for all Slobs CLI errors."""
+
+    def __init__(self, message: str):
+        super().__init__(message)
+        self.exit_code = 1
+
+    def show(self):
+        """Display the error message in red."""
+        click.secho(f"Error: {self.message}", fg="red", err=True)