Add free user limit pre-enforcement alert

What does this MR do and why?

Add free user limit pre-enforcement alert

Adds a pre-enforcement alert component to notify Free-tier private group namespaces above the user limit and storage limit about the 5-user limit enforcement

The pre-enforcement alerts are gated behind the free_user_cap_pre_enforcement_banner feature flag

Depends on !237120 (merged)

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/477232+

Screenshots or screen recordings

user	UI	Copy
Group owner		Your namespace free user limit test is over the 5 user limit Free top-level namespaces with private visibility cannot have more than 5 users. From August 15, 2026, if your namespace has more than 5 users, it will be placed in a read-only state. To prevent this, reduce the number of users in the namespace, make the namespace public, upgrade to a paid tier, or start a free 30-day Ultimate trial. Primary CTA: Explore paid plans Secondary CTA: Contact sales
Non group owner		Your namespace free user limit test is over the 5 user limit Free top-level namespaces with private visibility cannot have more than 5 users. From August 15, 2026, if your namespace has more than 5 users, it will be placed in a read-only state. Contact your top-level group Owner to reduce the number of users in the namespace, make the namespace public, upgrade to a paid tier, or start a free 30-day Ultimate trial.

How to set up and validate locally

1. Start GDK in SaaS mode: export GITLAB_SIMULATE_SAAS=1

2. Create a Free-tier private top-level group

3. In the rails console:

   ::Gitlab::CurrentSettings.update!(dashboard_limit_enabled: true, dashboard_limit: 5)
   Plan.free.limits.update!(storage_size_limit: 30)
   group = Group.find <group_id> # group you created in step 2
   group.root_storage_statistics.update!(storage_size: 35.megabytes)

4. Verify setup before continuing

   ::Namespaces::FreeUserCap::RootSize.new(group).above_size_limit? # should return true

5. Navigate to any page in the group (e.g. group members page): verify that the pre-enforcement banner is not shown (because the user count is below the limit)

6. Add 5 members to the group so the member count exceeds the dashboard limit (6+ users)

7. Refresh the page: verify the pre-enforcement banner is still not shown (banner FF is disabled)

8. In the rails console, enable the pre-enforcement banner FF, and ensure the enforcement FF is disabled

   Feature.enable(:free_user_cap_pre_enforcement_banner, group)
   Feature.disable(:free_user_cap_without_storage_check, group)

9. Refresh the page: verify that the pre-enforcement owner banner appears

   1. Sign in as a non-owner of the group: verify the non owner pre-enforcement banner appears

MR acceptance checklist

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