E-Mail-Retry, Voucher-Resend, Tageslimit, Docker-Politur

- Mailer::send mit Retry (2 Versuche); SMTP-Test & Templates waren bereits da
- admin/vouchers.php: Code per E-Mail (erneut) versenden (ajax_resend)
- Tageslimit Voucher pro Nicht-Admin-Benutzer (Setting + Durchsetzung in index)
- Docker: HEALTHCHECK (health.php) + curl; GHCR-Publish-Workflow
- Setting user_daily_voucher_limit + enforce in integrations.php

phpunit.xml.dist

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         failOnWarning="true">
+    <testsuites>
+        <testsuite name="unit">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>