Instruct AI agents to select and use MR description templates

What does this MR do and why?

Updates .ai/merge-requests.md so AI agents (Duo developer flow, Claude Code, etc.) base merge request descriptions on a template from .gitlab/merge_request_templates/ instead of inventing their own structure.

The current guidance only asks for a References heading and quick commands, so agent-authored MRs (for example !252554) end up missing template sections like Screenshots or screen recordings, How to set up and validate locally, and MR acceptance checklist.

The new guidance:

• Tells the agent to list .gitlab/merge_request_templates/ at runtime and choose the most specific match, so the instructions do not go stale as templates change.
• Defaults to Default.md when no specific template fits.
• Tells the agent to keep all template sections, filling each in or noting why it does not apply.

References

• Discussed in the context of !252554, where the developer flow produced a description without the Default template sections.

Screenshots or screen recordings

Not applicable, agent instruction file change only.

How to set up and validate locally

Not applicable. Ask an AI agent to open an MR in this repo and verify the description follows the appropriate template.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.