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

src/test-setup.ts

@@ -0,0 +1,10 @@
+import { getTestBed } from '@angular/core/testing';
+import {
+  BrowserDynamicTestingModule,
+  platformBrowserDynamicTesting,
+} from '@angular/platform-browser-dynamic/testing';
+
+getTestBed().initTestEnvironment(
+  BrowserDynamicTestingModule,
+  platformBrowserDynamicTesting(),
+);