Terminal locks up (non-recoverable) when listing Bedrock Agents during 'add agent' import on Windows 11

## Description

On Windows 11 (both Windows PowerShell and CMD), AgentCore CLI 0.25.0 hangs at multiple points in the interactive `add agent` flow. The most severe is a full, non-recoverable terminal lockup when the CLI attempts to list Bedrock Agents to import. `Ctrl+C` / `Ctrl+X` do not kill the CLI — the terminal has to be closed.

## Steps to Reproduce

From inside an existing AgentCore project with valid credentials:

1. Run `agentcore`
2. Select `add`
3. Select `agent`
4. Enter agent name: `MyAgent`
5. Select agent type: **Import from Bedrock Agents**
6. Select AWS region: **US East (N. Virginia) (us-east-1)**
7. The next screen (listing the Bedrock Agents) locks up the terminal.

## Expected Behavior

The screen should list the available Bedrock Agents for import, and the CLI should remain responsive. `Ctrl+C` should cancel/exit the CLI at any prompt.

## Actual Behavior

The Bedrock Agents listing screen hangs and locks up the terminal. The lockup appears non-recoverable — `Ctrl+C` and `Ctrl+X` do not kill the CLI, requiring the terminal to be force-closed.

## CLI Version

0.25.0

## Operating System

Windows

## Additional Context

- Reproduced on Windows 11 in both Windows PowerShell and CMD.
- Reporter notes "a few hang points" in the flow; the Bedrock Agents listing lockup above is the most severe (non-recoverable).
- `Ctrl+C` not cancelling prompts suggests the interactive prompt/signal handling may not be wired up for the Windows console.

Start by reproducing the interactive `add agent` flow on Windows 11 in both PowerShell and CMD, focusing on the Bedrock Agents listing step and Ctrl+C handling. Trace the CLI's prompt and signal-handling entry points to identify why the terminal becomes unresponsive; done means agents are listed, the terminal remains responsive, and Ctrl+C cancels the flow.

Written by the indexing model from the issue text.