--no-remote flag does not fully disable remote control

### Describe the bug

The `--no-remote` flag is documented as "Disable remote control of your session from GitHub web and mobile", but it only sets remote to read-only instead of fully disconnecting it. The /remote off slash command correctly disconnects, but `--no-remote` does not match this behavior.

### Affected version

Copilot CLI v1.0.37

### Steps to reproduce the behavior

1. Launch `copilot --no-remote`
2. Run `/remote` to check status
3. Observe: `Remote control status: read-only`

### Expected behavior

`/remote` should show `Remote control status: disconnected`, matching the behavior of `/remote off`.

### Additional context

There is also no persistent setting in `~/.copilot/settings.json` to default remote to disconnected, so users must run `/remote off` manually every session.

Start with the CLI argument handling for `copilot --no-remote` and the `/remote` status and `/remote off` command paths. Reproduce the issue on Copilot CLI v1.0.37 or the current version, then verify that launching with `--no-remote` reports `Remote control status: disconnected` rather than `read-only`.

索引モデルが issue の本文から書いたものです。