feat: restructure test infrastructure with unit/integration/system separation

Test Organization:
- Create tests/unit/, tests/integration/, tests/system/ directories
- Move existing tests into appropriate categories
- Add pytest markers (@pytest.mark.unit, @pytest.mark.integration)

Shared Fixtures:
- Create conftest.py with SQLite engine (for unit tests)
- Add PostgreSQL session fixture with transaction rollback
- Add TestClient fixture for API tests

Configuration:
- Update pyproject.toml with asyncio_mode=auto
- Add test markers and default addopts
- Add aiosqlite dependency for SQLite support

E2E Testing:
- Initialize Playwright in e2e/ directory
- Add playwright.config.ts
- Create login flow E2E test

Build:
- Add test-unit, test-integration, test-system, test-e2e to Makefile
- Update test target to run all categories
- Add testing documentation to README

Note: Some tests have import issues due to missing python-jose
package in dev environment. This needs to be addressed separately.

apps/api/tests/integration/test_seed.py

@@ -0,0 +1,59 @@
+from collections.abc import AsyncIterator
+
+import pytest
+import pytest_asyncio
+from sqlalchemy import select, text
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+
+from src.config import build_database_url
+from src.models.user import User
+from src.scripts.seed import build_seed_user, seed_database
+
+
+TEST_DATABASE_URL = build_database_url(
+    user="headquarter",
+    password="headquarter",
+    host="localhost",
+    port=5432,
+    database="headquarter",
+)
+
+
+@pytest_asyncio.fixture
+async def db_session() -> AsyncIterator[AsyncSession]:
+    engine = create_async_engine(TEST_DATABASE_URL)
+    session_factory = async_sessionmaker(engine, expire_on_commit=False)
+
+    async with session_factory() as session:
+        await session.execute(text("TRUNCATE TABLE git_repositories, projects, users RESTART IDENTITY CASCADE"))
+        await session.commit()
+        yield session
+        await session.execute(text("TRUNCATE TABLE git_repositories, projects, users RESTART IDENTITY CASCADE"))
+        await session.commit()
+
+    await engine.dispose()
+
+
+n@pytest.mark.integration
+
+def test_build_seed_user_returns_deterministic_payload() -> None:
+    payload = build_seed_user()
+
+    assert payload == {
+        "email": "dev@headquarter.local",
+        "name": "Development User",
+        "authentik_id": "dev-authentik-user",
+        "avatar_url": None,
+    }
+
+
+@pytest.mark.asyncio
+n@pytest.mark.integration
+
+async def test_seed_database_creates_development_user(db_session: AsyncSession) -> None:
+    await seed_database(db_session)
+
+    seeded_user = await db_session.scalar(select(User).where(User.email == "dev@headquarter.local"))
+
+    assert seeded_user is not None
+    assert seeded_user.authentik_id == "dev-authentik-user"