Fix Organizations pages under the Vue 3 rollout

What does this MR do and why?

Fixes the organization pages when running on Vue3.

1. The Organizations entry points create new VueApollo(...) but never call Vue.use(VueApollo). On Vue 2 this works because the super sidebar installs VueApollo globally. On Vue 3 the page has its own copy of the plugin, which stays inert until installed, so $apollo is undefined. This also breaks the organization users list and organizations list (no data), and settings, new organization, edit group and leaving an organization (fail on save/submit).
2. The groups and projects router used base: '/' with a single route /, so the current URL never matched. Vue Router 3 tolerated this. Vue Router 4 throws No match for {"query":{"display":"projects"}...} when the switcher pushes a query.

References

• Rollout issue: #631477
• Precedent: fdc802d6

Screenshots or screen recordings

None. Behavior is covered by the new feature spec.

How to set up and validate locally

1. Run gdk config set vite.vue_version 2, gdk reconfigure and gdk restart, so migrated pages run on Vue 3 while the rest stays on Vue 2, like production.
2. In a Rails console, run Feature.enable(:vue3_migrate_organizations).
3. Visit /o/default/-/groups_and_projects and confirm the console shows [V] Using Vue.js 3 (with @vue/compat) for OrganizationsGroupsAndProjects.
4. Confirm groups load. Switch the display to Projects and confirm projects load.

MR acceptance checklist

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