`calendar.createEvent` tool enforces `dateTime` requirement, preventing all-day event creation

The calendar.createEvent tool currently requires the dateTime property in the start and end parameters. According to the Google Calendar API documentation, all-day events are created by providing a date string (formatted as YYYY-MM-DD) and omitting the dateTime field.

Source: https://developers.google.com/workspace/calendar/api/guides/create-events states:

Specify timed events using the start.dateTime and end.dateTime fields. For all-day events, use start.date and end.date instead.

When attempting to create an all-day event by providing date but not dateTime, the tool returns a validation error: params/start must have required property 'dateTime'.

Steps to Reproduce

1. Attempt to create an event using calendar.createEvent.
2. Provide start: { date: "2026-01-26" } and end: { date: "2026-01-27" }.
3. The tool fails with a schema validation error: params/start must have required property 'dateTime'.

Expected Behavior

The tool should allow the date property as an alternative to dateTime (making both optional but requiring at least one), enabling the creation and modification of all-day events as supported by the underlying Google Calendar API.

Impact

Users cannot use the agent to manage all-day events. This forces the agent to use timed slots (e.g., 09:00 - 17:00) as a workaround, which clutters the user's schedule grid.

Start in workspace-server/src/services/CalendarService.ts at the schema linked in the issue, then reproduce the validation failure with the all-day start and end values shown. Done means calendar.createEvent accepts date-based all-day events while retaining support for timed events.