_merge_ical_properties() only handled a subset of event fields, silently
dropping categories, recurrence_rule, attendees, and reminder_minutes
during updates. These fields were fully supported by _create_ical_event()
and accepted by the MCP tool, but never applied.
Closes#544
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Chris Coutinho