docs: add Bilig WorkPaper MCP example

[gregkonush]

Why are these changes needed?

Adds a small autogen-ext MCP workbench example for a third-party stdio MCP server. The example uses Bilig WorkPaper to show an AutoGen workflow that can:

• launch an MCP server with McpWorkbench
• discover workbook tools
• read workbook input and summary ranges
• update an input cell
• verify recalculated formula readback
• confirm JSON persistence

The default path is a no-key smoke test. The optional --agent path uses AssistantAgent with the same MCP workbench and fails early with clear dependency/API-key guidance when optional agent dependencies or OPENAI_API_KEY are missing.

Related Bilig evaluator

Bilig has a copy-paste agent/MCP evaluator page for the same workbook proof pattern used here: tool discovery, cell mutation, formula readback, JSON export, and restore proof.
https://proompteng.github.io/bilig/eval-agent-mcp.html

Related issue number

N/A. Documentation/example-only contribution.

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed. GitGuardian and license/cla were passing on GitHub before the latest package-proof refresh.

Passing local validation:

python -m py_compile python/packages/autogen-ext/examples/bilig_workpaper_mcp_example.py
ruff format --check python/packages/autogen-ext/examples/bilig_workpaper_mcp_example.py
ruff check python/packages/autogen-ext/examples/bilig_workpaper_mcp_example.py
uv run --with autogen-core --with 'autogen-ext[mcp]' python python/packages/autogen-ext/examples/bilig_workpaper_mcp_example.py
npm view @bilig/workpaper version
npm exec --yes --package @bilig/workpaper@latest -- bilig-agent-challenge --json

npm view @bilig/workpaper version returned 0.119.0 in the 2026-05-29 refresh. The package proof command returned verified: true with formula readback, export, and restore checks passing.

The MCP smoke path verified ARR changed from 60000 to 96000 after setting Inputs!B3 to 0.4, expected customers changed to 8, persistence was true, restored readback matched, and the WorkPaper JSON was exported.

Expected guard-path validation:

env -u OPENAI_API_KEY uv run --with autogen-core --with 'autogen-ext[mcp]' python python/packages/autogen-ext/examples/bilig_workpaper_mcp_example.py --agent

That command exits with Error: Set OPENAI_API_KEY before running the optional --agent demo., which is the intended failure mode for the optional LLM-backed path without credentials.

[gregkonush]

@microsoft-github-policy-service agree