feat: comprehensive test infrastructure improvements

- Fix unit test imports: add env setup in conftest.py before module imports
- Add 24 new auth router tests (RBAC, preferences, password validation)
- Add 16 new tests for litellm and chat_summary routers
- Apply black formatting and ruff linting across codebase
- Add pre-commit hooks configuration (black, ruff, file checks)
- Increase CI coverage threshold from 40% to 50%

Test Results:
- 206 tests passing (91 unit + 115 integration)
- Coverage: 58.79% on core modules
- auth.py: 57% → 85%, litellm.py: 23% → 87%, chat_summary.py: 41% → 100%
- auth_service: 96.51%, config: 100%, rbac: 93.48%

dashboard/backend/tests/integration/test_litellm.py

@@ -0,0 +1,78 @@
+"""
+Integration tests for LiteLLM health check operations.
+"""
+import pytest
+from unittest.mock import AsyncMock, patch
+
+
+class TestLiteLLMHealth:
+    """Test LiteLLM health check endpoint."""
+
+    @pytest.mark.asyncio
+    async def test_health_check_success(self, test_app, mock_config, admin_headers, monkeypatch):
+        """Test successful health check."""
+        monkeypatch.setenv("LITELLM_URL", "http://mock-litellm:4000")
+        monkeypatch.setenv("LITELLM_HEALTH_API_KEY", "")
+
+        # Mock successful response
+        mock_response = AsyncMock()
+        mock_response.is_success = True
+        mock_response.status_code = 200
+
+        with patch("httpx.AsyncClient") as mock_client:
+            mock_client.return_value.__aenter__.return_value.get.return_value = mock_response
+
+            response = test_app.get("/api/litellm/health", headers=admin_headers)
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["ok"] is True
+        assert data["status"] == "up"
+        assert "latency_ms" in data
+        assert data["http_status"] == 200
+
+    @pytest.mark.asyncio
+    async def test_health_check_auth_required(self, test_app, mock_config, admin_headers, monkeypatch):
+        """Test health check when auth is required but not provided."""
+        monkeypatch.setenv("LITELLM_URL", "http://mock-litellm:4000")
+        monkeypatch.setenv("LITELLM_HEALTH_API_KEY", "")
+
+        # Mock 401 response without API key
+        mock_response = AsyncMock()
+        mock_response.is_success = False
+        mock_response.status_code = 401
+
+        with patch("httpx.AsyncClient") as mock_client:
+            mock_client.return_value.__aenter__.return_value.get.return_value = mock_response
+
+            response = test_app.get("/api/litellm/health", headers=admin_headers)
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["ok"] is True
+        assert data["status"] == "auth_required"
+        assert data["http_status"] == 401
+
+    @pytest.mark.asyncio
+    async def test_health_check_connection_error(self, test_app, mock_config, admin_headers, monkeypatch):
+        """Test health check when connection fails."""
+        monkeypatch.setenv("LITELLM_URL", "http://mock-litellm:4000")
+        monkeypatch.setenv("LITELLM_HEALTH_API_KEY", "")
+
+        # Mock connection error
+        with patch("httpx.AsyncClient") as mock_client:
+            mock_client.return_value.__aenter__.return_value.get.side_effect = Exception("Connection refused")
+
+            response = test_app.get("/api/litellm/health", headers=admin_headers)
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["ok"] is False
+        assert data["status"] == "down"
+        assert "Connection refused" in data["error"]
+
+    def test_health_check_without_auth(self, test_app, mock_config):
+        """Test health check without authentication."""
+        response = test_app.get("/api/litellm/health")
+
+        assert response.status_code == 401