Add CI/CD pipeline with automated testing and SFTP deployment

Introduces GitHub Actions workflows for continuous integration and
deployment. CI runs PHP linting (7.4, 8.1, 8.3), PHPCS with WordPress
coding standards, PHPUnit tests across PHP versions, and JS syntax
checks. Deployment to Hostinger via FTPS triggers on push to main
after all CI checks pass, with optional LiteSpeed cache purge.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

phpunit.xml.dist

@@ -0,0 +1,26 @@
+<?xml version="1.0"?>
+<phpunit
+    bootstrap="tests/bootstrap.php"
+    backupGlobals="false"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+>
+    <testsuites>
+        <testsuite name="unit">
+            <directory suffix="Test.php">./tests/unit</directory>
+        </testsuite>
+    </testsuites>
+
+    <coverage processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">./includes</directory>
+            <directory suffix=".php">./admin</directory>
+            <directory suffix=".php">./public</directory>
+        </include>
+        <exclude>
+            <directory suffix=".php">./admin/partials</directory>
+        </exclude>
+    </coverage>
+</phpunit>