Pass instance_beta_features_enabled to AI Catalog frontend

What does this MR do and why?

Related to !226615 (merged), which adds two gating mechanisms for MCP-related tools in Agent Catalog (comment):

1. instance_beta_features_enabled — experimental namespace setting
2. mcp_catalog_agent_tools — feature flag being added in %18.10

This MR passes instance_beta_features_enabled to the three AI Catalog frontend entry points (explore catalog, project agents platform, group agents platform) so the UI can conditionally show MCP-related features.

The value depends on deployment type:

• SaaS: checks per-namespace experiment_features_enabled setting via Ai::Catalog.user_can_access_experimental_and_beta_features?
• Self-managed/Dedicated: checks instance_level_ai_beta_features_enabled on Gitlab::CurrentSettings

Also moves Ai::Catalog.user_can_access_experimental_and_beta_features? from private to public so helpers and views can call it directly.

References

• Issue: #584281 (closed)
• Related MR: !226615 (merged)

How to set up and validate locally

GDK mode setup

SaaS mode:

1. Add GITLAB_SIMULATE_SAAS: '1' under the env: key in ~/gdk/gdk.yml:

   env:
     GITLAB_SIMULATE_SAAS: '1'

2. Run gdk reconfigure && gdk restart
3. Seed the Duo group if you haven't already:

   GITLAB_SIMULATE_SAAS=1 bundle exec 'rake gitlab:duo:setup'

4. Verify in Rails console: Gitlab.com? should return true

Self-managed mode:

1. Remove GITLAB_SIMULATE_SAAS from ~/gdk/gdk.yml (or set it to '0')
2. Run gdk reconfigure && gdk restart
3. Verify in Rails console: Gitlab.com? should return false

Toggle the settings

How to verify in Chrome

Navigate to the page, then View Page Source and search for instance-beta-features-enabled. The attribute appears on the mount element in the raw HTML:

• AI Catalog (/explore/ai-catalog) — look for <div id="js-ai-catalog" data-...instance-beta-features-enabled="true"...>

Screenshots

SAAS MODE

Experimental Settings	HTML DIV!

Self-Managed Mode

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