fix(mcp): prove stdio initialize compatibility (#199)

[rodboev]

Summary

Add focused coverage for the MCP stdio initialize path before changing runtime behavior. The local SDK handshake passes on the head branch, so the honest outcome is a scoped harness plus a documented external boundary rather than a runtime fix claim.

Refs #199

Root cause

skillspector mcp delegates stdio startup directly to FastMCP, and the repository has no focused initialize proof around that path. The earlier docs PR covered installing the MCP extra, but it did not establish that the stdio server responds to initialize in the reported environment.

Diff Notes

• Add a bounded MCP SDK stdio initialize test or harness for the SkillSpector server.
• Keep the runtime surface unchanged because the harness passes locally.
• Keep Codex-client success as a separate externally owned claim unless tested with Codex.

Scope

No MCP HTTP transport expansion, analyzer changes, graph changes, credential changes, or broad process-manager rewrite.

Verification

• .\.venv\Scripts\python.exe -m pytest tests/unit/test_mcp_server.py -k "initialize"
• .\.venv\Scripts\python.exe -m pytest tests/unit/test_mcp_server.py
• uv run ruff check src/ tests/
• uv run ruff format --check src/ tests/