Issue 2: Tear down legacy resource group (container apps and related resources)

### Background
Due to the reorganization of the authentication related web pages, the resources in the old resource group (container apps etc.) are no longer in use and should be removed.

### Tasks

- [ ] Confirm database migration is complete (#2145)
- [ ] Inventory all resources in the group and verify nothing else is still active (check logs/metrics for traffic)
- [ ] Check for cross-resource dependencies (managed identities, DNS entries, Key Vault, App Insights)
- [ ] Delete the resource group
- [ ] Verify no alerts/monitoring dashboards reference deleted resources

**Blocked by:** #2145

Start by confirming that database migration issue #2145 is complete, then inventory the legacy resource group and inspect logs and metrics for traffic. Check dependencies involving managed identities, DNS entries, Key Vault, and App Insights before deletion. Done means the group is safely removed and no alerts or monitoring dashboards reference its resources.

Written by the indexing model from the issue text.