Add generic worker tool sets to chat

[nishu-builder]

Summary

• add --tools <source> to chat, talk, and the TUI for selecting tracked, std-published, or hash-addressed worker-tool sets
• register each selected tool with an Anthropic-compatible tool.json containing exactly name, description, and input_schema, plus a separate Caos image executor binding
• pass the model-supplied JSON directly at /cas/args/in and pass the current workspace separately at /cas/args/workspace as execution context
• show selected workers alongside project tools in the TUI and document the generic registration and result contract
• add an end-to-end fixture proving selection, dispatch, result folding, and omission without --tools

Verification

• cargo test -p caos
• cargo test -p worker-llm-step
• cargo clippy -p caos -p worker-llm-step --all-targets -- -D warnings
• nix build
• built deployment completed and published refs/caos/bins and refs/caos/std
• caos-cli run-tool test --only=worker-tools currently cannot start the test suite because the mainline testenv image fails its Nix build: /homeless-shelter violates the no-sandbox purity check and the failure path then cannot find grep; this is outside this diff