docs: Claude Code and Codex guides don't mention the tool CLI / mcp serve route #1651

Found during the v0.12.9 release review (#1647).

docs/docs/usage/tool.md covers tool context, tool run and mcp serve, but the Claude Code and Codex guides under data-engineering/guides/ don't point to them as a route that needs no plugin, and the Codex guide doesn't show the plugin install the home-screen tip suggests (#1625). The tool daemon status/stop paragraph in tool.md is also dense.

Deferred: docs follow-up, no behaviour change.