Fix VueRouterCompat redirect handling and initial URL update

What does this MR do and why?

Fixes two related issues in the Vue Router 3→4 compatibility layer (VueRouterCompat):

1. Child catch-all redirects not matching empty paths: In Vue Router 3, a child * route with a redirect would match when the parent path was visited with no trailing child segment (e.g., visiting / would match * and redirect). Vue Router 4's :pathMatch(.*)* does NOT match the empty string in child routes. This MR adds an empty-path sibling route with the same redirect to preserve Vue Router 3 behavior.

2. Browser URL not updating on initial redirect: VueRouterCompat synchronously sets router.currentRoute.value to the redirect-resolved route so that components reading $route in data() see the correct value immediately. However, this prevents Vue Router 4's install() from running its initial async navigation (it checks currentRoute.value === START_LOCATION_NORMALIZED and skips if already changed). That initial navigation is what updates the browser URL via history.replace(). This MR adds a history.replace(resolved.fullPath) call after following redirects to ensure the browser URL reflects the final destination.

These issues were discovered while enabling Vue 3 compat mode for the Compliance Center, where visiting /groups/:group/-/security/compliance_dashboard should redirect to .../compliance_dashboard/dashboard but the URL was not being updated.

References

Related to the Vue 3 migration effort.

How to set up and validate locally

1. Run Vue 3 compat tests:

   VUE_VERSION=3 yarn jest spec/frontend/lib/utils/vue3compat/vue_router_spec.js --no-coverage

2. Run Vue 2 tests (should also pass):

   yarn jest spec/frontend/lib/utils/vue3compat/vue_router_spec.js --no-coverage

3. All 26 tests should pass in both modes.

MR acceptance checklist

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