Add PHPUnit tests with coverage for all src classes

- 21 test files covering controllers, services, entities, enums, messages
- CI: add test job with Xdebug coverage (clover + text)
- SonarQube: configure coverage report path and test sources

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -93,6 +93,25 @@ jobs:
       - name: Security audit
         run: composer audit
 
+  test:
+    runs_on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.4'
+          extensions: intl, pdo_pgsql, zip, gd, redis, imagick
+          coverage: xdebug
+
+      - name: Install dependencies
+        run: composer install --no-interaction --prefer-dist
+
+      - name: Run PHPUnit with coverage
+        run: vendor/bin/phpunit --testdox --coverage-clover coverage.xml --coverage-text
+
   sonarqube:
     runs_on: ubuntu-latest
     steps: