Add repo foundation: proxmox/lxc/vms groups, ansible.cfg, collections, lint configs

- inventory: add proxmox host, lxc and vms groups, critical_services per host
- retarget bootstrap and time-region to ubuntu:rocky so the Proxmox host is untouched
- add ansible.cfg, collections/requirements.yml, .gitignore, .yamllint, .ansible-lint
- remove stale root new_lxc.yml duplicate and the Nextcloud upgrade playbook

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JEczyvRjfakkiDNkbZA7PR

collections/requirements.yml

@@ -0,0 +1,7 @@
+---
+# Semaphore installs these automatically before each run
+# (it only looks at collections/requirements.yml and roles/requirements.yml).
+# Unpinned on purpose until the Semaphore ansible-core version is known.
+collections:
+  - name: community.general
+  - name: ansible.posix