git-remote-codecommit incompatible with aws login command - returns 403 error

### Summary
`git-remote-codecommit` fails with 403 error when using credentials authenticated via the `aws login` command (introduced in AWS CLI v2.32.0). The tool cannot read the credentials stored by `aws login`, making it incompatible with this new authentication method.

### Environment
- **AWS CLI Version:** aws-cli/2.32.21 Python/3.13.11 Windows/11 exe/AMD64
- **git-remote-codecommit Version:** Version: 1.17
- **Python Version:** Python 3.12.2
- **Operating System:** Windows 11
- **Git Version:**

### Steps to Reproduce

1. Install AWS CLI v2.32.0 or later
2. Authenticate using the new `aws login` command:
```bash
aws login --profile login-profile
```
(Browser opens, authentication succeeds)

3. Configure git remote using codecommit protocol:
```bash
git remote add aws codecommit://login-profile@repo
```

4. Attempt to fetch from the repository:
```bash
git fetch aws
```

### Expected Behavior
The git fetch should succeed, using the credentials obtained via `aws login`.

### Actual Behavior
The fetch fails with a 403 Forbidden error:
```
fatal: unable to access 'codecommit://login-profile@repo/': The requested URL returned error: 403
```

### Root Cause Analysis
The `aws login` command (AWS CLI v2.32.0+) uses browser-based OAuth authentication and stores credentials in a different location/format than traditional AWS credentials. `git-remote-codecommit` attempts to read credentials from:
- `~/.aws/credentials`
- `~/.aws/config` (standard profiles)
- SSO session cache (when configured via `aws configure sso`)

However, `aws login` stores credentials in a format that `git-remote-codecommit` does not recognize or cannot access.

### Workarounds

**Option 1: Use IAM User Credentials**
```bash
aws configure --profile login-profile
# Enter access key ID and secret access key when prompted
```

**Option 2: Use AWS SSO (Identity Center)**
```bash
aws configure sso --profile login-profile
# Follow prompts to configure SSO
aws sso login --profile login-profile
```

Both workarounds store credentials in formats that `git-remote-codecommit` can read.

### Documentation References
- `aws login` documentation: https://docs.aws.amazon.com/signin/latest/userguide/command-line-sign-in.html
- `git-remote-codecommit` setup: https://docs.aws.amazon.com/codecommit/latest/userguide/setting-up-git-remote-codecommit.html

### Related Issues
- #36 - Issues with new AWS CLI v2.9.x config formats
- #6 - CLI v2 support request

### Proposed Solution
`git-remote-codecommit` should be updated to:
1. Detect and read credentials stored by `aws login`
2. Support the OAuth-based credential format
3. Or, at minimum, provide a clear error message directing users to use `aws configure` or `aws configure sso` instead

Alternatively, AWS documentation should explicitly state that `aws login` is not compatible with `git-remote-codecommit` and users should use alternative authentication methods.

### Impact
- **Severity:** Medium - Users can work around this with alternative auth methods
- **Frequency:** Likely to increase as `aws login` is promoted as the recommended authentication method
- **User Experience:** Confusing for new users who follow the latest AWS CLI authentication guidance

### Additional Context

I discovered this issue while trying to use the new `aws login` command as
documented in the official AWS CLI documentation. The documentation suggests
`aws login` as the recommended method for console credential users, but this
creates an incompatibility with git-remote-codecommit.

This is particularly confusing because:
1. AWS promotes `aws login` as the easiest way to get started
2. CodeCommit documentation recommends git-remote-codecommit for federated access
3. There's no warning that these two features are incompatible