/kanban-add

Add a new card to the kanban board.

Instructions

1. Verify KANBAN.md exists in the current working directory. If not, tell the user to run /kanban-init first.
2. Read KANBAN.md.
3. Ask the user for:
   • Card title (required)
   • Description (optional, defaults to empty)
   • Column (default: "To Do" — must be one of: To Do, In Progress, Done)
4. Add the card to the end of the chosen column, using this format:

   ### Card title
   Description text here.
   
   ---
   

   Insert the card block just before the next ## column heading (or end of file if it's the last column). Make sure there is a blank line before the next ## heading.
5. Write the updated content back to KANBAN.md.
6. Confirm what was added and to which column.