Add attenu-guard integration page

[rafaelasor]

Adds integrations/attenu-guard.md for attenu-guard, an Apache-2.0 library
that gives each Haystack Agent/AgentTool sub-agent only the authority
its task needs and checks every tool call against it before the tool body
runs. It hooks Tool.invoke/invoke_async and the before_tool
ConfirmationStrategy protocol, using only public Haystack extension
points.

The usage snippet is a self-contained, offline scripted-model example: a
coordinator delegates to a sub-agent with a narrower authority, the
sub-agent's model tries to export data it was never granted, and the
export is denied before the tool body runs — verified runnable against
haystack-ai 3.1.0 and attenu-guard 0.8.0.

Disclosure: I maintain attenu-guard.

[vercel]

@rafaelasor is attempting to deploy a commit to the deepset Team on Vercel.

A member of the Team first needs to authorize it.

[rafaelasor]

The Vercel preview is waiting on a team member to authorize the deploy, so the red check is not about the page itself. Can someone on the team approve it, or is the preview not needed for an integration page?

[rafaelasor]

@kacperlukawski Ignore my note about the Vercel check. #584, #557, #547 and #567 all merged with it red, so it gates the fork preview and not the merge.

On need: a Haystack sub-agent reached through AgentTool keeps its own tool list, so it can hold permissions its caller never had. The adapter makes the child's a subset of the parent's and denies crm_export before the tool body runs. The demo in the library shows that end to end, offline and with no API key.

I can add logos/attenu-guard.png and the logo: field in a second commit.