Restructure compose mirror: stacks/ grouped by purpose, not by host

Replaces rocky-docker-lxc/, caddy-vm/, monitoring-vm/, and automation/
with a single stacks/ tree grouped by function (identity-and-security,
platform, media, productivity, dev-tools) - 55 stacks total, every one
a real directory in the private repos today.

Resolves all outstanding drift: adds Wazuh (previously entirely
missing), Firefly III and Postiz (never mirrored), the internal-zone
Caddy instance and the Cron Scheduler's separate NocoDB instance
(both previously conflated with their counterparts under one shared
folder); renames Calibre-Web to calibre-web-automated and splits
Kodi-MariaDB into kodi + mariadb-latest to match what the private
repos actually run now; drops the decommissioned NetBox stack.

Also removes automation/iac/old-content/ and
automation/ansible/old-playbooks/ in the same pass - both folders
were entirely stale content describing a superseded architecture
(GitLab instead of Gitea, HAProxy+mTLS SSO instead of the current
Caddy+Authentik setup), now replaced by docs/iac-pipeline.md.

stacks/platform/mysql-8/docker-compose.yaml

@@ -0,0 +1,15 @@
+services:
+  mysql-8:
+    container_name: mysql-8
+    image: mysql:8
+    restart: "no"
+    environment:
+      # No real data lives here - a thin self-hosted-registry mirror build
+      # target, not a running database.
+      - MYSQL_RANDOM_ROOT_PASSWORD=yes
+    healthcheck:
+      test: ["CMD-SHELL", "mysqladmin ping -h 127.0.0.1 || exit 1"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+      start_period: 20s