Automatically tag runner with gitlab--duo during AI development setup

Problem Statement

Running rake setup_ai_development and choosing "yes" to configure the runner creates it without the gitlab--duo tag. This tag was recently added in gitlab!213431 (merged) and is required for Remote Flows in Duo Agent Platform.

Impact

Remote Flows fail without the tag, so engineers must manually add it after setup.

Proposal

Update lib/tasks/runner.rake to automatically add tag_list: ['gitlab--duo'] during runner creation.

Impacted categories

The following categories relate to this issue:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.