test: add comprehensive tests for ClaudeCodeProvider

Addresses code review feedback about missing automated tests for the ClaudeCodeProvider.

## Changes

- Added unit tests for ClaudeCodeProvider class covering constructor, validateAuth, and getClient methods
- Added unit tests for ClaudeCodeLanguageModel testing lazy loading behavior and error handling
- Added integration tests verifying optional dependency behavior when @anthropic-ai/claude-code is not installed

## Test Coverage

1. **Unit Tests**:
   - ClaudeCodeProvider: Basic functionality, no API key requirement, client creation
   - ClaudeCodeLanguageModel: Model initialization, lazy loading, error messages, warning generation

2. **Integration Tests**:
   - Optional dependency behavior when package is not installed
   - Clear error messages for users about missing package
   - Provider instantiation works but usage fails gracefully

All tests pass and provide comprehensive coverage for the claude-code provider implementation.

tests/unit/ai-providers/claude-code.test.js

@@ -0,0 +1,104 @@
+import { jest } from '@jest/globals';
+
+// Mock the claude-code SDK module
+jest.unstable_mockModule('../../../src/ai-providers/custom-sdk/claude-code/index.js', () => ({
+	createClaudeCode: jest.fn(() => {
+		const provider = (modelId, settings) => ({
+			// Mock language model
+			id: modelId,
+			settings
+		});
+		provider.languageModel = jest.fn((id, settings) => ({ id, settings }));
+		provider.chat = provider.languageModel;
+		return provider;
+	})
+}));
+
+// Mock the base provider
+jest.unstable_mockModule('../../../src/ai-providers/base-provider.js', () => ({
+	BaseAIProvider: class {
+		constructor() {
+			this.name = 'Base Provider';
+		}
+		handleError(context, error) {
+			throw error;
+		}
+	}
+}));
+
+// Import after mocking
+const { ClaudeCodeProvider } = await import('../../../src/ai-providers/claude-code.js');
+
+describe('ClaudeCodeProvider', () => {
+	let provider;
+
+	beforeEach(() => {
+		provider = new ClaudeCodeProvider();
+		jest.clearAllMocks();
+	});
+
+	describe('constructor', () => {
+		it('should set the provider name to Claude Code', () => {
+			expect(provider.name).toBe('Claude Code');
+		});
+	});
+
+	describe('validateAuth', () => {
+		it('should not throw an error (no API key required)', () => {
+			expect(() => provider.validateAuth({})).not.toThrow();
+		});
+
+		it('should not require any parameters', () => {
+			expect(() => provider.validateAuth()).not.toThrow();
+		});
+
+		it('should work with any params passed', () => {
+			expect(() => provider.validateAuth({
+				apiKey: 'some-key',
+				baseURL: 'https://example.com'
+			})).not.toThrow();
+		});
+	});
+
+	describe('getClient', () => {
+		it('should return a claude code client', () => {
+			const client = provider.getClient({});
+			expect(client).toBeDefined();
+			expect(typeof client).toBe('function');
+		});
+
+		it('should create client without API key or base URL', () => {
+			const client = provider.getClient({});
+			expect(client).toBeDefined();
+		});
+
+		it('should handle params even though they are not used', () => {
+			const client = provider.getClient({
+				baseURL: 'https://example.com',
+				apiKey: 'unused-key'
+			});
+			expect(client).toBeDefined();
+		});
+
+		it('should have languageModel and chat methods', () => {
+			const client = provider.getClient({});
+			expect(client.languageModel).toBeDefined();
+			expect(client.chat).toBeDefined();
+			expect(client.chat).toBe(client.languageModel);
+		});
+	});
+
+	describe('error handling', () => {
+		it('should handle client initialization errors', async () => {
+			// Force an error by making createClaudeCode throw
+			const { createClaudeCode } = await import('../../../src/ai-providers/custom-sdk/claude-code/index.js');
+			createClaudeCode.mockImplementationOnce(() => {
+				throw new Error('Mock initialization error');
+			});
+
+			// Create a new provider instance to use the mocked createClaudeCode
+			const errorProvider = new ClaudeCodeProvider();
+			expect(() => errorProvider.getClient({})).toThrow('Mock initialization error');
+		});
+	});
+});