test: httpapi-mcp status test is not hermetic against user-global MCP config

Found during v0.9.2 release verification. Deferred because: pre-existing (fails identically at v0.9.1), passes in CI's clean env; fixing test fixtures mid-release adds risk.

`test/server/httpapi-mcp.test.ts` "serves status endpoint" expects only the fixture `demo` server, but a user-global MCP config (e.g. `codebase-memory-mcp`) leaks into the status response on dev machines, failing the test locally. The fixture should isolate config discovery (scoped config dir / env) so the suite is hermetic.