Initial commit: webtrees Email Newsletter module

Recurring email newsletter for webtrees 2.2+. Each enabled tree
sends upcoming birthdays of living individuals, optional marriage
anniversaries of intact couples, and a once-per-calendar-month
historical section of births and deaths of deceased individuals.

Triggered exclusively by an external scheduler (system cron,
systemd timer, etc.) hitting a token-gated HTTP endpoint — never
on visitor page loads. The "is it due?" decision is idempotent
within the configured frequency window.

Per-user subscription is integrated into the built-in
/my-account/{tree} page via a custom view + a decorated
AccountUpdate handler. Admins can add external addresses and
trigger an immediate send for testing. Email body renders in
German for German-language users; English otherwise. Birthdays
and anniversaries are formatted with the upcoming-event ordinal
age (e.g. "45th birthday" / "45. Geburtstag").

LICENSE

@@ -0,0 +1,9 @@
+                    GNU AFFERO GENERAL PUBLIC LICENSE
+                       Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies of this
+ license document, but changing it is not allowed.
+
+The full text of the GNU Affero General Public License v3.0 is
+available at <https://www.gnu.org/licenses/agpl-3.0.txt>.