[BUG] RuntimeClientError when invoking agent deployed using Starter kit direct code deployment option

**Describe the bug**
Invoking agent deployed using Starter kit `direct code deployment ` option results in `RuntimeClientError`. This may be caused due to

**To Reproduce**
Steps to reproduce the behavior:
1. Follow instructions using starter kit available here: [Get started with Amazon Bedrock AgentCore Runtime direct code deployment](https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/runtime-get-started-code-deploy.html)
2. Invoke agent using `agentcore invoke '{"prompt":"Tell me a joke"}'`

**Expected behavior**
Agent responds with LLM generated joke.

**Error Output**
```
Invocation failed: An error occurred (RuntimeClientError) when calling the InvokeAgentRuntime operation: Runtime initialization time exceeded. Please make sure that initialization completes in 60s.
```

**Environment:**
- OS: macOS 26.0
- Python version: 3.13
- Package version: [e.g. 0.1.0]
- Installation method: agentcore starter kit

**Additional context**
Possible reasons for failure
* Incorrect starter-kit auto generated Agentcore Runtime IAM execution role
* `uv pip install --target` used by starter-kit adds absolute path to python interpreter from local environment to packaged binaries. Workaround, use `pip install --target`.

Follow the linked Amazon Bedrock AgentCore Runtime direct code deployment guide and reproduce the failure with `agentcore invoke '{"prompt":"Tell me a joke"}'`. Inspect the starter-kit-generated runtime role and the packaging step using `uv pip install --target`, then compare the result with `pip install --target`; done means the deployed agent initializes within 60 seconds and returns a joke.

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