Increment 1 - Step 6: Unit & Integration Testing

[angelobarbu]

Step 6: Unit & Integration Testing

First test suite for every layer of the stack, built entirely on Qt Test — and with it, the project's last source-level dependency removed.

What's new

• Unit tests (Qt Test, one QObject class per binary): modulo_core_tests (project version), modulo_api_health_dto_tests / modulo_api_error_dto_tests (DTO round-trips, rejection of missing/mistyped fields), modulo_api_json_tests (api::json::require* never falls back to QJson's silent defaults), modulo_server_config_tests (defaults, every variable, empty-means-unset, port 0, malformed ports → config.invalid_port). Data-driven cases use _data() slots.
• Integration test modulo_integration_tests: a real QHttpServer on an OS-assigned loopback port with a real QNetworkAccessManager client — /api/v1/health body and version, and the 404 JSON error envelope. Opt-in via MODULO_TEST_DB_URL; otherwise it QSKIPs and CTest reports Skipped, so ctest --preset all never needs Docker to pass.
• QML smoke test modulo_client_qml_tests via QUICK_TEST_MAIN, run offscreen automatically.
• tests/support/include/modulo/testing/integration.h — shared fixtures (MODULO_REQUIRE_TEST_DATABASE(), blocking httpGet() with timeout).
• Removed Catch2 dependency