Vue 3 migration: deployment details (show) page

What does this MR do and why?

Adds the vue3_migrate_deployments feature flag and a vue3_migration.yml for the deployment details (show) page. It opts into Option 1: the bundler builds a Vue 2 and a Vue 3 chunk, and Rails serves the Vue 3 chunk only when the flag is on (default-off).

One entrypoint, pages/projects/deployments/show, mounting the ~/deployments/show app (ShowDeploymentRoot, Apollo) via initVueApp. status: rollout behind vue3_migrate_deployments.

Risk

Low. The ~/deployments tree (5 components + utils) and the shared SPA machinery were audited against the real Vue 2→3 breakers: data() is a function throughout, no removed filters: component option, no Vue.extend/propsData/Vue.observable/$children/local functional components. The mount already uses initVueApp. No cross-team popover blocker applies (the reference popovers aren't wired up on this page). Covered by spec/frontend/deployments (green under Vue 3).

References

• Migration issue: Vue 3 migration: deployment details (show) page (#629158)
• Epic: &23285

Screenshots or screen recordings

Vue 3 walkthrough video to be attached.

How to set up and validate locally

1. Enable the flag:

   Feature.enable(:vue3_migrate_deployments)

2. Visit a deployment, e.g. /<project>/-/environments/:environment_id/deployments/:iid. Confirm the console shows [V] Using Vue.js 3 for ShowDeploymentRoot.
3. Confirm the header, aside, and deploy block render and the deployment/environment/release Apollo data loads.
4. Run VUE_VERSION=3 yarn jest spec/frontend/deployments.

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.