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were entirely stale content describing a superseded architecture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/postgres-18-alpine/docker-compose.yaml

@@ -0,0 +1,17 @@
+services:
+  postgres-18-alpine:
+    container_name: postgres-18-alpine
+    image: postgres:18-alpine
+    restart: "no"
+    environment:
+      # No real data lives here - a thin self-hosted-registry mirror build
+      # target so other stacks can pull the result. trust auth is fine
+      # since nothing reaches it but the health check below - Postgres
+      # refuses to start at all without some password/auth method set.
+      - POSTGRES_HOST_AUTH_METHOD=trust
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+      start_period: 10s