CLI broken (functionality does not work) on Windows: "'charmap' codec can't encode character"

### Describe the bug

Running the following on Windows (in PowerShell or in Git Bash for Windows) produces a Python character encoding error. This implies that the Python library is assuming a charset rather than specifying wone.

```bash
aws agent-toolkit list-available-skills
```

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Expected Behavior

The command `aws agent-toolkit list-available-skills` lists skills with no error.

### Current Behavior

```
{
"skills": [
…
{
"name": "amazon-documentdb",
"description":

aws: [ERROR]: 'charmap' codec can't encode character '\u2192' in position 249: character maps to
```

### Reproduction Steps

1. Open PowerShell or Git Bash for Windows on Windows 11.
2. Issue ` aws agent-toolkit list-available-skills`

### Possible Solution

There is no known solution at the time. The CLI is completely broken.

### Additional Information/Context

See [UnicodeEncodeError: 'charmap' codec can't encode characters](https://stackoverflow.com/questions/27092833/unicodeencodeerror-charmap-codec-cant-encode-characters) for possible background research.

This comes up in the AgentCore CLI as well; see aws/agentcore-cli#2010. The stack trace there indicated `…\.venv\Lib\site-packages\bedrock_agentcore\runtime\app.py:_sync_stream_with_error_handling:945`. There's no way to know without further investigation whether this is some shared AWS Python library, or bad Python Code AWS has duplicated across toolkits and/or CLIs, or what.

### CLI version used

aws-cli/2.36.23 Python/3.14.6 Windows/11 exe/AMD64

### Environment details (OS name and version, etc.)

Windows 11 Pro 25H2 26200.9168