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/pyproject.toml

@@ -0,0 +1,34 @@
+[project]
+name = "kmtnflower-backend"
+version = "1.0.0"
+requires-python = ">=3.12"
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+python_classes = ["Test*"]
+python_functions = ["test_*"]
+asyncio_mode = "auto"
+addopts = [
+    "--strict-markers",
+    "--strict-config",
+    "-v",
+]
+
+[tool.coverage.run]
+source = ["app"]
+branch = true
+omit = ["*/tests/*", "*/__pycache__/*", "seed.py", "inject_test_logs.py", "probe_geo.py"]
+
+[tool.coverage.report]
+show_missing = true
+skip_empty = true
+fail_under = 10
+exclude_lines = [
+    "pragma: no cover",
+    "if TYPE_CHECKING:",
+    "raise NotImplementedError",
+]
+
+[tool.coverage.html]
+directory = "htmlcov"