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/e2e/__init__.py

@@ -0,0 +1 @@
+# Placeholder for e2e tests package

tests/e2e/test_workflows/test_full_workflow.py

@@ -0,0 +1,22 @@
+"""E2E tests placeholder.
+
+These tests will verify complete workflows with real NotebookLM API.
+Requires authentication and should be run manually.
+"""
+
+import pytest
+
+
+@pytest.mark.e2e
+class TestFullWorkflow:
+    """End-to-end workflow tests."""
+
+    async def test_research_to_podcast_workflow(self):
+        """Should complete full research to podcast workflow."""
+        # TODO: Implement E2E test
+        # 1. Create notebook
+        # 2. Add sources
+        # 3. Generate audio
+        # 4. Wait for completion
+        # 5. Download artifact
+        pytest.skip("E2E tests require NotebookLM authentication")