docs(mcp): add reviewed host configurations

[adity982]

Problem and outcome

Alpha users had only one generic MCP host snippet. The MCP package README now starts from a locked source checkout and provides reviewed configurations for both the workspace package bin and the explicit built stdio entrypoint.

The guide also makes the three-tool read-only surface, local-process trust boundary, and external resource limits explicit.

Closes #9

Verification

• parsed all three JSON configuration blocks with Python's JSON parser
• verified both absolute-path placeholders and all local links
• git diff --check
• package build/test not run locally because Node/Corepack is unavailable on this host

Contract and risk review

• Graph IR and runtime behavior are unchanged
• no new tools, paths accepted from models, network access, secrets, or side effects
• documentation continues to reserve stdout for MCP JSON-RPC