test: add comprehensive test suite with 89% coverage

- Add tests for all backend modules: config, database, models, services,
  routes, middleware, and providers
- Separate dev dependencies using dependency-groups
- Update CLAUDE.md with test commands and project structure
- Add .coverage and .pytest_cache to gitignore

88 tests covering:
- Authentication and authorization
- Model routing and key selection
- Async logging with batch processing
- All API endpoints (chat, openai, anthropic, health)
- LiteLLM wrapper (mocked external calls)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_models.py

@@ -0,0 +1,118 @@
+"""Tests for data models."""
+import pytest
+from app.models import ClientKey, Provider, ProviderKey, RequestLog
+
+
+class TestClientKey:
+    """Test ClientKey model."""
+
+    def test_create_client_key(self):
+        """Test creating a ClientKey instance."""
+        key = ClientKey(
+            id=1,
+            key="test-key",
+            name="test-client",
+            is_active=True,
+            created_at="2024-01-01"
+        )
+        assert key.id == 1
+        assert key.key == "test-key"
+        assert key.name == "test-client"
+        assert key.is_active is True
+
+    def test_client_key_with_null_name(self):
+        """Test ClientKey with null name."""
+        key = ClientKey(
+            id=1,
+            key="test-key",
+            name=None,
+            is_active=True,
+            created_at="2024-01-01"
+        )
+        assert key.name is None
+
+
+class TestProvider:
+    """Test Provider model."""
+
+    def test_create_provider(self):
+        """Test creating a Provider instance."""
+        provider = Provider(
+            id=1,
+            name="openai",
+            base_url="https://api.openai.com/v1",
+            api_type="openai",
+            is_active=True
+        )
+        assert provider.id == 1
+        assert provider.name == "openai"
+        assert provider.api_type == "openai"
+
+    def test_provider_anthropic(self):
+        """Test creating an Anthropic provider."""
+        provider = Provider(
+            id=2,
+            name="anthropic",
+            base_url="https://api.anthropic.com/v1",
+            api_type="anthropic",
+            is_active=True
+        )
+        assert provider.name == "anthropic"
+        assert provider.api_type == "anthropic"
+
+
+class TestProviderKey:
+    """Test ProviderKey model."""
+
+    def test_create_provider_key(self):
+        """Test creating a ProviderKey instance."""
+        key = ProviderKey(
+            id=1,
+            provider_id=1,
+            key="sk-test",
+            is_active=True,
+            created_at="2024-01-01"
+        )
+        assert key.id == 1
+        assert key.provider_id == 1
+        assert key.key == "sk-test"
+
+
+class TestRequestLog:
+    """Test RequestLog model."""
+
+    def test_create_request_log(self):
+        """Test creating a RequestLog instance."""
+        log = RequestLog(
+            id=1,
+            client_key_id=1,
+            provider_id=1,
+            model="gpt-4o",
+            prompt_tokens=10,
+            completion_tokens=20,
+            latency_ms=100,
+            success=True,
+            error_message=None,
+            created_at="2024-01-01"
+        )
+        assert log.model == "gpt-4o"
+        assert log.success is True
+        assert log.error_message is None
+
+    def test_request_log_with_error(self):
+        """Test RequestLog with error."""
+        log = RequestLog(
+            id=None,
+            client_key_id=1,
+            provider_id=1,
+            model="gpt-4o",
+            prompt_tokens=None,
+            completion_tokens=None,
+            latency_ms=100,
+            success=False,
+            error_message="Rate limit exceeded",
+            created_at=None
+        )
+        assert log.id is None
+        assert log.success is False
+        assert log.error_message == "Rate limit exceeded"