Style newsletters and system e-mails like www.eom.dev

Catppuccin Mocha campaign template (default) and archive variant, kept
in sync in the database; system e-mail header/footer overridden via
--static-dir from a ConfigMap. PNG logo for mail clients. Tested in
Mailpit (desktop, phone width; 87% CSS support, rest inlined).

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

templates/email-configmap.yml.j2

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: {{ listmonk_name }}-email-templates
+  namespace: {{ listmonk_namespace }}
+  labels:
+    app.kubernetes.io/name: listmonk
+    app.kubernetes.io/instance: {{ listmonk_name }}
+data:
+  # Overrides only this file; every other system template stays built in.
+  base.html: {{ lookup('ansible.builtin.template', 'email/base.html.j2') | to_json }}