Add infra/ with student-vms OpenTofu root module

- infra/pve: host facts, IP plan, one-time setup
- infra/tofu/student-vms: 3 student VMs via tf-mod-pve v1.0.0
- infra/sandbox: template clones for throwaway test VMs
- README/TODO: Windows DC/AD instead of FreeIPA, new network
- .gitignore: only ignore secrets.auto.tfvars instead of all tfvars

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TODO.md

@@ -1,11 +1,6 @@
 ## TODOs
 
-- [ ] change hostnames and correspondingly the dns entries of the student hosts to `vm_00` -> manage dns via opentofu 
-- [ ] include all users to freeipa and integrate freeipa as main identity and dns server. Deprecate current bind servers -> automate client installation
-- [ ] migrate dns zone to freeipa and manage its bind server with opentofu
-- [ ] create nfs shares for the home folder of each user
-- [ ] write loop for student_vm deployment -> they are similar
-
-- [ ] include automation which install freeipa-client on each vm via opentofu or ansible executed via opentofu
+- [ ] set up the Windows DC/AD `dc01` (`10.100.200.70`, 2 vCPU, 4-8 GB) as identity and DNS server
+- [ ] switch the student VMs' DNS to the DC and join them to the domain
+- [ ] create AD accounts and home folders for all students
 - [ ] write nice markdown template for sheets. With better code highlighting and better text formatting
-