Correct the common-ai toolset list and document the shields extra

[Lee-W]

The toolsets guide told readers that four toolsets were included, but documented seven. The three extra ones are not re-exported from the package root, so anyone importing them the way the first four are imported hits an ImportError with nothing in the guide to explain it. The extras list also never mentioned shields, leaving no way to find out which extra installs the guardrail support the agent guide describes.

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