Enable creation of timed calendar event from the grid

[victor-enogwe]

Summary

Implement the ability for users to create a timed calendar event directly from the Day view Agenda calendar surface grid.

Scope

• Allow users to click a cell in the grid to initiate event creation
• Display event creation modal pre-filled with data from the selection (date/time)
• Persist created event and reflect changes immediately on the grid
• Validate event data, handle errors, and provide feedback
• Support quick add (minimal fields) and advanced event creation

Acceptance Criteria

• User can create events from calendar grid (single click)
• Relevant modal fields are prefilled based on user interaction
• Persisted events reflected without reload
• Input validation and error handling included

Additional Context

• Leverage grid event creation patterns in codebase
• Reference UX flow and files for grid selection/interaction.