fix(cli): restore is_flag=False + flag_value on --cwd option

Reverts an earlier incorrect cleanup: click.option with
is_flag=False + flag_value="." is valid click syntax that
allows --cwd to work both with and without an argument:

  --cwd              → cwd="." (current directory)
  --cwd /path        → cwd="/path"
  --cwd=.            → cwd="."
  --cwd --flag       → cwd=".", flag=True (correctly parsed)

Without these parameters, --cwd requires a value and
--dangerously-skip-permissions would be misread as the cwd.

bin/cli.py

@@ -37,6 +37,8 @@ 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/).",