Add Deck workflow automation Nextcloud app

Ports the standalone due-date cron script into a proper Nextcloud 34
app with a personal-settings UI, per-user workflow configuration
(source/target stack, assigned-user and label filters, email
notification), a TimedJob background runner, and Gitea CI pipelines.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

phpunit.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd"
+         bootstrap="tests/bootstrap.php"
+         colors="true">
+	<testsuites>
+		<testsuite name="unit">
+			<directory>tests/Unit</directory>
+		</testsuite>
+	</testsuites>
+	<source>
+		<include>
+			<directory suffix=".php">lib</directory>
+		</include>
+	</source>
+</phpunit>