Fix: testy + bugfix SettingsRepository::allSettings() + migracja phpunit.xml

- SettingsRepository::allSettings() — inicjalizacja $settings = [] przed pętlą
  (bug: false ?? [] zwracało false gdy cache pusty a DB null)
- Stuby wydzielone do tests/stubs/CacheHandler.php + S.php
- phpunit.xml zmigurowany do schematu PHPUnit 10 (coverage → source)
- composer.lock dodany do repozytorium

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

phpunit.xml

@@ -1,20 +1,14 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
-         bootstrap="tests/bootstrap.php"
-         colors="true">
-
+<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>
-
-  <coverage>
+  <source>
     <include>
       <directory>autoload/Domain</directory>
       <directory>autoload/Shared</directory>
     </include>
-  </coverage>
-
+  </source>
 </phpunit>