Add drag-and-drop reordering to event funnel steps

[tudddorrr]

Drag-and-drop funnel step reordering

• Added grip icon handle on each funnel step that allows reordering via drag-and-drop using motion/react Reorder components
• Steps are wrapped in a Reorder.Group with Reorder.Item children, using a transient id field as the stable key for motion reconciliation
• prepareFunnelStep now strips the transient editor id before saving so it never reaches the server
• reorderFunnelSteps utility reorders steps array based on the ordered IDs returned by the Reorder component
• A new EditableFunnelStep type extends EventFunnelStep with a client-only id field, assigned via a simple incrementing counter