ci: run qmltestrunner with offscreen Qt platform

Headless CI runner has no X display, so qmltest aborts loading the
xcb plugin. Set QT_QPA_PLATFORM=offscreen for the ctest invocation
in CI and in both Makefile qmltest targets so local headless runs
work too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -79,6 +79,8 @@ jobs:
 
       - name: QML unit tests (qmltestrunner via Qt::QuickTest)
         working-directory: framework/qml
+        env:
+          QT_QPA_PLATFORM: offscreen
         run: |
           cmake -S . -B build-tests -DBUILD_TESTING=ON
           cmake --build build-tests --target qml_unit_tests --parallel

examples/todo/Makefile

@@ -93,4 +93,4 @@ quality: build qmltest ## Run PHPStan, php-cs-fixer (check), PHPUnit, qmllint, q
 qmltest: ## Run QML unit tests (Qt::QuickTest via qmltestrunner)
 	cmake -S ../../framework/qml -B ../../framework/qml/build-tests -DBUILD_TESTING=ON
 	cmake --build ../../framework/qml/build-tests --target qml_unit_tests --parallel
-	ctest --test-dir ../../framework/qml/build-tests --output-on-failure -R qml_unit_tests
+	QT_QPA_PLATFORM=offscreen ctest --test-dir ../../framework/qml/build-tests --output-on-failure -R qml_unit_tests

framework/skeleton/Makefile

@@ -87,4 +87,4 @@ quality: build qmltest ## Run PHPStan, php-cs-fixer (check), PHPUnit, qmllint, q
 qmltest: ## Run QML unit tests (Qt::QuickTest via qmltestrunner)
 	cmake -S ../qml -B ../qml/build-tests -DBUILD_TESTING=ON
 	cmake --build ../qml/build-tests --target qml_unit_tests --parallel
-	ctest --test-dir ../qml/build-tests --output-on-failure -R qml_unit_tests
+	QT_QPA_PLATFORM=offscreen ctest --test-dir ../qml/build-tests --output-on-failure -R qml_unit_tests