Add a tested Python MCP diagnostic example for the installed SDK

## Problem

A Python diagnostic for a Streamable HTTP Model Context Protocol (MCP) endpoint attempted to create the client with this unsupported call:

```python
streamable_http_client(..., headers=...)
```

The installed `mcp` package rejected the call before it contacted the endpoint. That package version requires request headers on an `httpx.AsyncClient` supplied through `http_client=`:

```python
streamable_http_client(
...,
http_client=httpx.AsyncClient(headers={...}),
)
```

This local API mismatch can be mistaken for a remote MCP server, authentication, or transport failure. NemoClaw does not have a checked-in Python diagnostic example and test that own this SDK compatibility contract.

## Product decision required

Before implementation, decide whether NemoClaw will own this diagnostic as:

1. A checked-in troubleshooting tool or example.
2. A documented example with an exact compatible SDK range.

The selected surface must have a named source of truth for its SDK version and an automated compatibility test. This issue is not an installer defect.

## Acceptance criteria

- The accepted design identifies the owning repository surface and the exact SDK version source of truth.
- With the supported SDK, the diagnostic configures request headers through the supported HTTP-client API.
- Against a local test server, the diagnostic completes MCP `initialize` and `tools/list` requests.
- A client-construction or SDK-signature failure is reported as a local dependency compatibility error.
- The diagnostic does not classify a local dependency compatibility error as a remote server, authentication, authorization, or transport failure.
- Diagnostic output does not contain authorization headers, access tokens, or other credential values.
- A deterministic test uses the repository-installed dependency and fails when an incompatible SDK API replaces the supported API.
- The owned tool or documentation states how to run the diagnostic and how to interpret its result.
- Acceptance does not require a live external MCP service.

## Related work

- #10944 owns NemoClaw MCP verification behavior when connection or authentication fails. This issue owns the separate diagnostic-client SDK compatibility contract.

## Scope boundary

- Do not change a remote MCP server or OpenShell protocol behavior in this issue.
- Do not add support for an SDK range without an accepted compatibility and maintenance policy.

Start by resolving the product decision between a checked-in troubleshooting tool/example and documentation, then identify the owning surface and SDK version source of truth. Use the repository-installed dependency with a local test server to verify MCP initialize and tools/list, and ensure compatibility failures are distinguished from remote failures without exposing credentials. Done means the chosen surface documents usage and interpretation and includes a deterministic compatibility test.

Written by the indexing model from the issue text.