Schedule Enhancements — Leave-only view and staff restrictions

New filtering and visibility options on the schedule screen. Managers can now toggle a "Show Leave Only" filter to see just leave entries. Staff users have a restricted view that shows only their own relevant schedule information, with leave type details hidden.

Key details:

• "Show Leave Only" toggle on the schedule
• Staff-appropriate schedule view (no sensitive leave details)
• Role filter on Manage Leave page