Correct paid tier shown for credits-backed items in More Features modal

What does this MR do and why?

Seven credits-backed menu items in the More Features (Feature Library) modal were missing a tier: attribute, causing them to render as "Free" instead of "Add-on". This MR sets tier: :add_on on each affected item so the frontend TIERS.ADD_ON enum match fires and the correct "Add-on" label is displayed.

Items fixed:

• secrets_manager in the project security and compliance menu
• secrets_manager in the group security and compliance menu
• agents_runs, ai_flow_triggers, ai_catalog_agents, ai_flows, ai_catalog_mcp_servers, agents_onboarding in the project Duo Agents menu
• ai_agents, ai_flows, ai_catalog_mcp_servers in the group Duo Agents menu
• Corrected the ai_catalog_mcp_servers description in the project Duo Agents menu from "Configure automation triggers" to "Connect MCP servers to extend agent tooling" (per reviewer feedback); locale/gitlab.pot regenerated accordingly

With the exception of the updated description, this is a backend data-only change. No frontend changes are needed because TIERS.ADD_ON = 'add_on' already exists in the frontend constants.

References

• Resolves #621943 (closed)

Screenshots or screen recordings

N/A - backend data change only; the "Add-on" label already renders correctly when tier: :add_on is set.

How to set up and validate locally

1. Open the More Features modal in the super sidebar.
2. Verify that Secrets Manager, AI Agents, AI Flows, MCP Servers, Sessions, Triggers, and Onboarding items now show "Add-on" instead of "Free".

MR acceptance checklist

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