chore: relocate .env to the repository root and refresh Make targets

.env is now consumed by both Ansible and OpenTofu, so keep a single copy at
the repo root instead of ansible/.env:

- rename ansible/.env.example -> .env.example.
- Makefile: ENV_FILE ?= $(REPO_ROOT)/.env (absolute, works from any cwd);
  REQUIRE_ENV/LOAD_ENV updated; help text.
- bootstrap-pve-api-token.yml / bootstrap-monitoring-pve-token.yml write and
  read ../../.env; bootstrap now keeps backup: true (it rewrites the whole
  file, clobbering MONITORING_*/EMERGENCY_*/PROXMOX_ROOT_PASSWORD).
- roles/pve_lxc, roles/monitoring_server: fail_msg points at the repo-root .env.

The Makefile also picks up the new targets added by later commits
(tofu-*, validate, pbs-storage, ru-vps-base, zerotier-decommission); they are
grouped here so all recipes land together.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uoq5AVK8mkBgg83Mq6o5V

ansible/playbooks/bootstrap-monitoring-pve-token.yml

@@ -5,7 +5,8 @@
   vars:
     monitoring_pve_user: monitoring@pve
     monitoring_pve_token_id: prometheus
-    monitoring_pve_env_file: "{{ playbook_dir }}/../.env"
+    # .env лежит в корне репозитория, playbook_dir — это ansible/playbooks.
+    monitoring_pve_env_file: "{{ playbook_dir }}/../../.env"
     monitoring_pve_rotate_existing_token: false
   tasks:
     - name: Read existing Proxmox users