Expose standalone typed tools in UK chat

[anth-volk]

Summary

Enable the UK chat runtime to expose the existing standalone typed tools directly to the model, while preserving run_python as the fallback path.

Scope

• Register typed tools for household calculation, economy-wide simulation, and allowed non-FRS microdata analysis.
• Keep FRS protected from row-level record exposure while allowing aggregate FRS simulation outputs.
• Update model-facing prompt guidance and runtime docs to explain when typed tools should be used.
• Keep frontend tool labels readable for the newly exposed tools.
• Add tests for tool exposure, FRS rejection, mocked non-FRS microdata behaviour, and prompt contracts.
• Reduce avoidable nondeterminism in chat/tool execution without adding a deterministic router yet.

Validation target

The branch should pass focused backend prompt/tool tests and frontend build, with full PR CI running against the repository workflow.