MCP: add project_id filter to get_schedule

get_schedule returns tasks/events/timeslots over a date range but has no project_id (label) parameter. Its only filters today are entities, overdue_mode, completed_mode, sort, and a filters object (guests / priority / duration / all-day).

Fix: an optional project_id (or project_ids[]) filter on get_schedule, alongside the existing filters, to enable per-project task pulls. get_task already covers single-id reads — the gap is for "all open tasks for one project."