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_ssh_keys_api.py

@@ -0,0 +1,26 @@
+import pytest
+from httpx import AsyncClient
+
+from src.main import app
+
+
+@pytest.fixture
+async def async_client():
+    async with AsyncClient(app=app, base_url="http://test") as client:
+        yield client
+
+
+@pytest.mark.asyncio
+n@pytest.mark.integration
+
+async def test_create_ssh_key_requires_authentication(async_client: AsyncClient) -> None:
+    response = await async_client.post("/ssh-keys", json={"name": "test-key"})
+    assert response.status_code == 401
+
+
+@pytest.mark.asyncio
+n@pytest.mark.integration
+
+async def test_list_ssh_keys_requires_authentication(async_client: AsyncClient) -> None:
+    response = await async_client.get("/ssh-keys")
+    assert response.status_code == 401