When --accept was passed after positional args (e.g., 'studio run --agent
carmack task --accept'), clap's trailing_var_arg captured it as part of
g3_args instead of parsing it as the studio flag. This caused g3 to error
with 'unexpected argument --accept'.
- Extract filter_accept_flag() helper to detect and remove --accept from
trailing args
- Set auto_accept=true if --accept found in either position
- Add 5 unit tests for the filtering logic