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/integration/claude-code-optional.test.js

@@ -0,0 +1,85 @@
+import { jest } from '@jest/globals';
+
+// Mock the base provider to avoid circular dependencies
+jest.unstable_mockModule('../../src/ai-providers/base-provider.js', () => ({
+	BaseAIProvider: class {
+		constructor() {
+			this.name = 'Base Provider';
+		}
+		handleError(context, error) {
+			throw error;
+		}
+	}
+}));
+
+// Mock the claude-code SDK to simulate it not being installed
+jest.unstable_mockModule('@anthropic-ai/claude-code', () => {
+	throw new Error("Cannot find module '@anthropic-ai/claude-code'");
+});
+
+// Import after mocking
+const { ClaudeCodeProvider } = await import('../../src/ai-providers/claude-code.js');
+
+describe('Claude Code Optional Dependency Integration', () => {
+	describe('when @anthropic-ai/claude-code is not installed', () => {
+		it('should allow provider instantiation', () => {
+			// Provider should instantiate without error
+			const provider = new ClaudeCodeProvider();
+			expect(provider).toBeDefined();
+			expect(provider.name).toBe('Claude Code');
+		});
+
+		it('should allow client creation', () => {
+			const provider = new ClaudeCodeProvider();
+			// Client creation should work
+			const client = provider.getClient({});
+			expect(client).toBeDefined();
+			expect(typeof client).toBe('function');
+		});
+
+		it('should fail with clear error when trying to use the model', async () => {
+			const provider = new ClaudeCodeProvider();
+			const client = provider.getClient({});
+			const model = client('opus');
+
+			// The actual usage should fail with the lazy loading error
+			await expect(model.doGenerate({
+				prompt: [{ role: 'user', content: 'Hello' }],
+				mode: { type: 'regular' }
+			})).rejects.toThrow("Claude Code SDK is not installed. Please install '@anthropic-ai/claude-code' to use the claude-code provider.");
+		});
+
+		it('should provide helpful error message for streaming', async () => {
+			const provider = new ClaudeCodeProvider();
+			const client = provider.getClient({});
+			const model = client('sonnet');
+
+			await expect(model.doStream({
+				prompt: [{ role: 'user', content: 'Hello' }],
+				mode: { type: 'regular' }
+			})).rejects.toThrow("Claude Code SDK is not installed. Please install '@anthropic-ai/claude-code' to use the claude-code provider.");
+		});
+	});
+
+	describe('provider behavior', () => {
+		it('should not require API key', () => {
+			const provider = new ClaudeCodeProvider();
+			// Should not throw
+			expect(() => provider.validateAuth()).not.toThrow();
+			expect(() => provider.validateAuth({ apiKey: null })).not.toThrow();
+		});
+
+		it('should work with ai-services-unified when provider is configured', async () => {
+			// This tests that the provider can be selected but will fail appropriately
+			// when the actual model is used
+			const provider = new ClaudeCodeProvider();
+			expect(provider).toBeDefined();
+			
+			// In real usage, ai-services-unified would:
+			// 1. Get the provider instance (works)
+			// 2. Call provider.getClient() (works)
+			// 3. Create a model (works)
+			// 4. Try to generate (fails with clear error)
+		});
+	});
+});