An event is editable now.

Summary of Changes

1. Event System for Cursor Positioning:

   • Added SetCursor(Option<Position>) to AppEvent enum
   • Added cursor position handling in App::draw()
   • Widgets can now request cursor positioning via events

2. Editable Event Widget:

   • Made title and date_time editable with tui-input
   • Added edit mode with e key to enter editing
   • Tab/Shift+Tab to switch between datetime and title fields
   • Enter to confirm, Esc to cancel
   • Input validation with error highlighting (red color)

3. Cursor Positioning:

   • Implemented centered cursor / input calculation to work correctly with centered text (via centered_input helper function)

4. Event Handling:

   • Updated TuiEvent to include Crossterm(CrosstermEvent) variant. Needed to proper event passing to tui-input for full input handling.

Last part to
close #93