'charmap' codec can't encode character '\U0001f680' in position 4: character maps to <undefined>

### Description

Running the bare AgentCore getting-started demo produces a Unicode error:

> 'charmap' codec can't encode character '\U0001f680' in position 4: character maps to

### Steps to Reproduce

Exactly following [Get started with the AgentCore CLI](https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/runtime-get-started-cli.html):

1. `npm install -g @aws/agentcore`
2. `agentcore create --name MyAgent --framework Strands --protocol HTTP --model-provider Bedrock --memory none`
3. In `MyAgent/model/load.py`, change the model:
> `return BedrockModel(model_id="global.amazon.nova-2-lite-v1:0")`
4. `cd MyAgent`
5. `agentcore dev`
6. Enter a question; e.g. "What are the highlights of the uv package manager for Python?"

### Expected Behavior

The model returns a response with no error.

### Actual Behavior

> The **uv** package manager for Python is an extremely fast, all-in-one tool that simplifies Python development by replacing multiple tools with a single, high-performance solution. Here are the key highlights of **uv**:
>
> ### 🚀 \*\*Error: 'charmap' codec can't encode character '\U0001f680' in position 4: character maps to <undefined>

### CLI Version

0.27.0

### Operating System

Windows

### Additional Context

Initial searches indicated this is related to Python. In any case, in an enterprise framework the first-steps demo should run without issue, across platforms.

From experience, I would guess that one or more layer is making assumptions about the system charset rather than being explicit about which charset is needed.

…

Looking at the console stack trace, the error seems to originate in: `MyAgent\\app\\MyAgent\\.venv\\Lib\\site-packages\\bedrock_agentcore\\runtime\\app.py:_sync_stream_with_error_handling:945`

Reproduce the Windows failure with the documented AgentCore CLI commands and inspect MyAgent/.venv/Lib/site-packages/bedrock_agentcore/runtime/app.py at _sync_stream_with_error_handling around line 945. Trace how streamed response text is written or encoded, then verify that the getting-started demo handles the 🚀 character without a Unicode error on Windows.

Written by the indexing model from the issue text.