Document and continuously verify the MCP contract

[sebawebber]

Parent

#43

What to build

Make the stable public MCP contract understandable to users and continuously
verifiable in CI. Documentation becomes the source of truth for connection,
inputs, results, errors, operational constraints, and intentionally deferred
work.

Acceptance criteria

• Public MCP documentation describes https://api.pgconfig.org/mcp, compatible client connection, the single tool, every input, normalization, defaults, Tuning Assumptions, warnings, errors, and the structured result.
• Documentation includes representative successful and invalid requests without duplicating implementation details.
• Documentation explains anonymous access, Origin restrictions, stateless execution, the timeout, and structured logging expectations.
• The README links to the MCP documentation instead of duplicating the complete contract.
• Deferred work records rationale and revisit triggers for caching, custom rate limiting, Prometheus metrics, authentication, additional tools, detailed calculation traces, pgBadger and log_format, decimal RAM, and listen_addresses review.
• A separate CI job runs the official MCP server conformance suite against the endpoint implementation with the conformance package version pinned.
• The normal Go test command remains free of Node dependencies.
• Documentation states that MCP Registry submission follows endpoint stabilization and does not block the initial deployment.

Blocked by

• Harden and observe public MCP execution #47