feat: add test framework, unit tests, and GitLab CI pipeline

- Add pytest config in backend/pyproject.toml with asyncio mode and coverage
- Add backend/requirements-test.txt with pytest, pytest-cov, pytest-asyncio, aiosqlite
- Write 86 backend unit tests covering auth (JWT tokens), schemas (Pydantic
  models), config (Settings env overrides), log_parser (log parsing, IP
  resolution, geo data), models (SQLAlchemy table definitions + column
  defaults), and theme export
- Add Vitest config for Angular frontend (vitest.config.ts, src/test-setup.ts)
- Add .gitlab-ci.yml with stages: backend-test, frontend-test, backend-lint,
  docker-build, and quality-gate
- CI enforces 10% minimum coverage threshold for backend

backend/tests/conftest.py

@@ -0,0 +1,21 @@
+"""Shared test fixtures for kmtnflower backend tests."""
+
+import pytest
+from unittest.mock import patch
+
+# Override settings for tests — use SQLite so we don't need PostgreSQL
+@pytest.fixture(autouse=True)
+def override_settings():
+    """Set test-only environment variables before any import of app modules."""
+    env = {
+        "KMTN_DATABASE_URL": "sqlite+aiosqlite:///:memory:",
+        "KMTN_ENV": "test",
+        "KMTN_JWT_SECRET_KEY": "test-secret-key-do-not-use",
+        "KMTN_ADMIN_USERNAME": "testadmin",
+        "KMTN_ADMIN_PASSWORD": "testpass123",
+        "KMTN_LOGS_DIR": "/tmp/kmtn_test_logs",
+        "KMTN_GEOLITE2_DB_PATH": "/nonexistent/GeoLite2-City.mmdb",
+        "KMTN_THEME_JSON_PATH": "/tmp/kmtn_test_theme.json",
+    }
+    with patch.dict("os.environ", env, clear=False):
+        yield env