bug: q login ignoring identity-provider/region flags

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

macOS 15.6.1

### Expected behaviour

If I pass in the `--identity-provider` or `--region` flag, I'd expect a browser window or automatic login.

### Actual behaviour

If I pass in the `--identity-provider` or `--region` flag, I'm given a prompt:

```
$ q login --license pro --identity-provider https://x-1234567890.awsapps.com/start --region us-east-1
✔ Enter Start URL · https://x-1234567890.awsapps.com/start
✔ Enter Region · us-east-1
```

### Steps to reproduce

I'm unsure if this is a bug or misconfiguration on my part. I did find these PR's indicating this should work:

- https://github.com/aws/amazon-q-developer-cli/issues/1082
- https://github.com/aws/amazon-q-developer-cli/pull/1112

### Environment

```yaml
$ q diagnostics

[q-details]
version = "1.19.3"
hash = "84b82da54996570ac369ec69911e29b524099761"
date = "2025-10-29T21:11:53.813462Z (6d ago)"
variant = "full"

[system-info]
os = "macOS 15.6.1 (24G90)"
chip = "Apple M4 Max"
total-cores = 14
memory = "36.00 GB"

[environment]
cwd = "/Users/USER/projects"
cli-path = "/Users/USER/projects"
os = "Mac"
shell-path = "/opt/homebrew/Cellar/fish/4.1.2/bin/fish"
shell-version = "4.1.2"
terminal = "Ghostty"
install-method = "brew"

[env-vars]
PATH = "/Users/USER/.pyenv/shims:/Users/USER/.local/bin:/Users/USER/.asdf/shims:/Users/USER/.pyenv/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/Users/USER/.krew/bin:/Users/USER/go/bin:/Applications/Ghostty.app/Contents/MacOS:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/homebrew/bin:/opt/podman/bin:/Users/USER/.local/bin"
QTERM_SESSION_ID = "0eb418e4ca7e41dd82fe635bdc52f992"
Q_PARENT = ""
Q_TERM = "1.19.3"
SHELL = "/bin/zsh"
TERM = "xterm-ghostty"
__CFBundleIdentifier = "com.mitchellh.ghostty"
```