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/conftest.py

@@ -0,0 +1,168 @@
+"""Test configuration and shared fixtures."""
+import asyncio
+import pytest
+import aiosqlite
+from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock
+from contextlib import asynccontextmanager
+
+# Test database path
+TEST_DB_PATH = Path(__file__).parent / "data" / "test.db"
+
+
+@asynccontextmanager
+async def get_test_db():
+    """Get in-memory test database connection."""
+    conn = await aiosqlite.connect(":memory:")
+    conn.row_factory = aiosqlite.Row
+    await _init_test_schema(conn)
+    await _seed_test_data(conn)
+    yield conn
+    await conn.close()
+
+
+async def _init_test_schema(db: aiosqlite.Connection):
+    """Initialize test database schema."""
+    await db.executescript("""
+        CREATE TABLE IF NOT EXISTS client_keys (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            key TEXT UNIQUE NOT NULL,
+            name TEXT,
+            is_active BOOLEAN DEFAULT TRUE,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS providers (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            name TEXT UNIQUE NOT NULL,
+            base_url TEXT NOT NULL,
+            api_type TEXT NOT NULL,
+            is_active BOOLEAN DEFAULT TRUE
+        );
+
+        CREATE TABLE IF NOT EXISTS provider_keys (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            provider_id INTEGER NOT NULL REFERENCES providers(id),
+            key TEXT NOT NULL,
+            is_active BOOLEAN DEFAULT TRUE,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS request_logs (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            client_key_id INTEGER REFERENCES client_keys(id),
+            provider_id INTEGER REFERENCES providers(id),
+            model TEXT,
+            prompt_tokens INTEGER,
+            completion_tokens INTEGER,
+            latency_ms INTEGER,
+            success BOOLEAN,
+            error_message TEXT,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+    """)
+
+
+async def _seed_test_data(db: aiosqlite.Connection):
+    """Seed test data."""
+    # Seed providers
+    await db.executemany(
+        "INSERT INTO providers (name, base_url, api_type) VALUES (?, ?, ?)",
+        [
+            ("openai", "https://api.openai.com/v1", "openai"),
+            ("anthropic", "https://api.anthropic.com/v1", "anthropic"),
+        ]
+    )
+    # Seed client keys
+    await db.execute(
+        "INSERT INTO client_keys (key, name, is_active) VALUES (?, ?, ?)",
+        ("test-api-key", "test-client", True)
+    )
+    await db.execute(
+        "INSERT INTO client_keys (key, name, is_active) VALUES (?, ?, ?)",
+        ("disabled-key", "disabled-client", False)
+    )
+    # Seed provider keys
+    await db.execute(
+        "INSERT INTO provider_keys (provider_id, key, is_active) VALUES (?, ?, ?)",
+        (1, "sk-openai-key-1", True)
+    )
+    await db.execute(
+        "INSERT INTO provider_keys (provider_id, key, is_active) VALUES (?, ?, ?)",
+        (1, "sk-openai-key-2", True)
+    )
+    await db.execute(
+        "INSERT INTO provider_keys (provider_id, key, is_active) VALUES (?, ?, ?)",
+        (2, "sk-ant-key-1", True)
+    )
+    await db.commit()
+
+
+@pytest.fixture
+def mock_db(monkeypatch):
+    """Mock database connection for tests."""
+    @asynccontextmanager
+    async def mock_db_connection():
+        async with get_test_db() as db:
+            yield db
+
+    monkeypatch.setattr("app.database.db_connection", mock_db_connection)
+    return mock_db_connection
+
+
+@pytest.fixture
+def mock_litellm():
+    """Mock LiteLLM completion."""
+    mock_response = MagicMock()
+    mock_response.usage = MagicMock()
+    mock_response.usage.prompt_tokens = 10
+    mock_response.usage.completion_tokens = 20
+    mock_response.model_dump.return_value = {
+        "id": "chatcmpl-test",
+        "object": "chat.completion",
+        "choices": [{"message": {"content": "test response"}}]
+    }
+
+    async def mock_acompletion(*args, **kwargs):
+        return mock_response
+
+    return {"acompletion": mock_acompletion, "response": mock_response}
+
+
+@pytest.fixture
+def client_key():
+    """Return a test client key instance."""
+    from app.models import ClientKey
+    return ClientKey(
+        id=1,
+        key="test-api-key",
+        name="test-client",
+        is_active=True,
+        created_at="2024-01-01 00:00:00"
+    )
+
+
+@pytest.fixture
+def provider():
+    """Return a test provider instance."""
+    from app.models import Provider
+    return Provider(
+        id=1,
+        name="openai",
+        base_url="https://api.openai.com/v1",
+        api_type="openai",
+        is_active=True
+    )
+
+
+@pytest.fixture
+def provider_key():
+    """Return a test provider key instance."""
+    from app.models import ProviderKey
+    return ProviderKey(
+        id=1,
+        provider_id=1,
+        key="sk-test-key",
+        is_active=True,
+        created_at="2024-01-01 00:00:00"
+    )