Check default duo namespace minimum access level setting

What does this MR do and why?

As a follow-up to !218864 (comment 3038791220), in this MR we check the user's default Duo namespace's access level setting instead of the current namespace's access level setting when using Agentic Chat on a public group or project where the user is a non member.

This is part of Role-based permissions DAP - Foreground execute... (#578554 - closed) to implement a role based permission check for Agentic Chat access on .com.

This feature is behind a feature flag

References

• Role-based permissions DAP - Foreground execute... (#578554 - closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

Testing instructions listed on !218864 (merged)

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