v0.3.0

At start-up the server checks, at most once a day, whether a newer release is on PyPI, and tells the agent so it can mention it; it never upgrades itself. The check is turned off with AVENIR_MCP_NO_UPDATE_CHECK=1, DO_NOT_TRACK=1 or in CI (#66). On a read-only server, no tool description names a hidden write tool. See CHANGELOG.md.