Add four reminder scheduling affordances to the canvas:
- Floating 📅 icon on selected shapes toggles the reminder widget
- Right-click "Schedule a reminder" context menu option
- Drag-to-calendar compact mode (shows after 200ms of shape movement)
- Email notification via EncryptID on reminder creation
Closes TASK-122
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
