fix(calendar): address PR feedback from maintainer

- Remove CHANGELOG.md changes (auto-generated from commits)
- Move all parameter descriptions into function docstrings for LLM context
- Remove unused caldav dependency (using httpx for CalDAV implementation)
- Move datetime imports to top of modules
- Remove load_dotenv from tests/conftest.py
- Clarify Event vs Meeting distinction in docstrings
- Handle 401 auth errors gracefully in calendar tests

Addresses all feedback from PR #95 review

tests/integration/test_calendar_operations.py

@@ -95,6 +95,10 @@ async def test_list_calendars(nc_client: NextcloudClient):
     calendars = await nc_client.calendar.list_calendars()
 
     assert isinstance(calendars, list)
+    
+    if not calendars:
+        pytest.skip("No calendars available - Calendar app may not be enabled")
+    
     logger.info(f"Found {len(calendars)} calendars")
 
     # Check structure of calendars