Logs a new time entry into Toggl.
LLM Notes:
- Always use the get_tags tool first to find a matching existing tag before calling this tool.
- Always check with get_entry_descriptions tool to see if there's a very similar description that exists and use that as the description.

@param start_time the start datetime in ET (New York) e.g., "2026-03-07T07:30:00"
@param end_time the end datetime in ET (New York) e.g., "2026-03-07T07:30:00"
@param description the activity performed e.g., "Walked dog"
@param tag the tag associated with the entry e.g., "chore"
@returns a time entry object. Make sure to review it for what was actually added.