Add PHPStan report for SonarQube analysis

- Add sonar.php.phpstan.reportPaths to sonar-project.properties
- Generate phpstan-report.json in CI php job, sonarqube job, and sonarqube.yml workflow

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

.gitea/workflows/sonarqube.yml

@@ -67,6 +67,9 @@ jobs:
       - name: JS tests with coverage
         run: bun run test:coverage
 
+      - name: PHPStan report
+        run: vendor/bin/phpstan analyse src/ --level=6 --no-progress --error-format=json > phpstan-report.json || true
+
       - name: Build assets
         run: bun run build