Fix: projects can use duo features if parent has Duo disabled

What does this MR do and why?

Fix: projects can use duo features if parent has Duo disabled

• Projects can override the Duo setting of the parent value. For example, a root group might disable Duo by default but projects can selectively enable.
• Before this change, disabled parent would disable Agentic Chat for all children.

References

• Confidential issue (customer report): https://gitlab.com/gitlab-org/gitlab/-/issues/570062

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Run GDK in SaaS Mode
• Gdk Duo Agentic Chat working in web, see !197267 (merged) for how
• Disable Duo Features at the root group level ("off by default")
• Enable Duo Features for a project in the group
• Agentic Chat should be available on the project (before this MR, it wasn't)

MR acceptance checklist

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