feat(api): implement notebook management CRUD endpoints

Implement Sprint 1: Notebook Management CRUD

- Add NotebookService with full CRUD operations
- Add POST /api/v1/notebooks (create notebook)
- Add GET /api/v1/notebooks (list with pagination)
- Add GET /api/v1/notebooks/{id} (get by ID)
- Add PATCH /api/v1/notebooks/{id} (partial update)
- Add DELETE /api/v1/notebooks/{id} (delete)
- Add Pydantic models for requests/responses
- Add custom exceptions (ValidationError, NotFoundError, NotebookLMError)
- Add comprehensive unit tests (31 tests, 97% coverage)
- Add API integration tests (26 tests)
- Fix router prefix duplication
- Fix JSON serialization in error responses

BREAKING CHANGE: None

tests/unit/test_core/test_exceptions.py

@@ -0,0 +1,161 @@
+"""Tests for core exceptions."""
+
+import pytest
+
+from notebooklm_agent.core.exceptions import (
+    AuthenticationError,
+    NotebookLMAgentError,
+    NotebookLMError,
+    NotFoundError,
+    RateLimitError,
+    ValidationError,
+    WebhookError,
+)
+
+
+@pytest.mark.unit
+class TestNotebookLMAgentError:
+    """Test suite for base exception."""
+
+    def test_default_code(self):
+        """Should have default error code."""
+        # Arrange & Act
+        error = NotebookLMAgentError("Test message")
+
+        # Assert
+        assert error.code == "AGENT_ERROR"
+        assert str(error) == "Test message"
+
+    def test_custom_code(self):
+        """Should accept custom error code."""
+        # Arrange & Act
+        error = NotebookLMAgentError("Test message", code="CUSTOM_ERROR")
+
+        # Assert
+        assert error.code == "CUSTOM_ERROR"
+
+
+@pytest.mark.unit
+class TestValidationError:
+    """Test suite for ValidationError."""
+
+    def test_default_details(self):
+        """Should have empty details by default."""
+        # Arrange & Act
+        error = ValidationError("Validation failed")
+
+        # Assert
+        assert error.code == "VALIDATION_ERROR"
+        assert error.details == []
+
+    def test_with_details(self):
+        """Should store validation details."""
+        # Arrange
+        details = [{"field": "title", "error": "Required"}]
+
+        # Act
+        error = ValidationError("Validation failed", details=details)
+
+        # Assert
+        assert error.details == details
+
+
+@pytest.mark.unit
+class TestAuthenticationError:
+    """Test suite for AuthenticationError."""
+
+    def test_default_message(self):
+        """Should have default error message."""
+        # Arrange & Act
+        error = AuthenticationError()
+
+        # Assert
+        assert error.code == "AUTH_ERROR"
+        assert str(error) == "Authentication failed"
+
+    def test_custom_message(self):
+        """Should accept custom message."""
+        # Arrange & Act
+        error = AuthenticationError("Custom auth error")
+
+        # Assert
+        assert str(error) == "Custom auth error"
+
+
+@pytest.mark.unit
+class TestNotFoundError:
+    """Test suite for NotFoundError."""
+
+    def test_message_formatting(self):
+        """Should format message with resource info."""
+        # Arrange & Act
+        error = NotFoundError("Notebook", "abc123")
+
+        # Assert
+        assert error.code == "NOT_FOUND"
+        assert error.resource == "Notebook"
+        assert error.resource_id == "abc123"
+        assert "Notebook" in str(error)
+        assert "abc123" in str(error)
+
+
+@pytest.mark.unit
+class TestNotebookLMError:
+    """Test suite for NotebookLMError."""
+
+    def test_stores_original_error(self):
+        """Should store original exception."""
+        # Arrange
+        original = ValueError("Original error")
+
+        # Act
+        error = NotebookLMError("NotebookLM failed", original_error=original)
+
+        # Assert
+        assert error.code == "NOTEBOOKLM_ERROR"
+        assert error.original_error is original
+
+
+@pytest.mark.unit
+class TestRateLimitError:
+    """Test suite for RateLimitError."""
+
+    def test_default_values(self):
+        """Should have default message and no retry_after."""
+        # Arrange & Act
+        error = RateLimitError()
+
+        # Assert
+        assert error.code == "RATE_LIMITED"
+        assert str(error) == "Rate limit exceeded"
+        assert error.retry_after is None
+
+    def test_with_retry_after(self):
+        """Should store retry_after value."""
+        # Arrange & Act
+        error = RateLimitError(retry_after=60)
+
+        # Assert
+        assert error.retry_after == 60
+
+
+@pytest.mark.unit
+class TestWebhookError:
+    """Test suite for WebhookError."""
+
+    def test_without_webhook_id(self):
+        """Should work without webhook_id."""
+        # Arrange & Act
+        error = WebhookError("Webhook failed")
+
+        # Assert
+        assert error.code == "WEBHOOK_ERROR"
+        assert error.webhook_id is None
+
+    def test_with_webhook_id(self):
+        """Should store webhook_id."""
+        # Arrange & Act
+        error = WebhookError("Webhook failed", webhook_id="webhook123")
+
+        # Assert
+        assert error.webhook_id == "webhook123"