fix(cli): remove invalid --cwd flag config and make upgrade a proper alias

- Remove is_flag=False + flag_value="." combination which has no effect
  on click option with is_flag=False (default)
- Create dedicated click.Command for upgrade instead of raw alias
  assignment, so help shows correct command name

bin/cli.py

@@ -37,8 +37,6 @@ def _resolve_chat_cwd() -> Path:
 @click.option(
     "--cwd",
     "-C",
-    is_flag=False,
-    flag_value=".",
     default=None,
     type=click.Path(dir_okay=True, file_okay=False),
     help="Use specified path as working directory (default: workspace/).",