Add confirmation step on kit creation (fixes #5566)

[rodrigovirgilio]

Resolves #5566

Description

• Adds a confirmation modal on kit creation showing the kit name, value, and item/quantity list, with the note that item composition can't be edited after saving (fixes Add a confirmation step on kit entry #5566).
• "No, I need to make changes" dismisses the modal and returns to the form with all values intact; "Yes, it's correct" proceeds to save.
• Preserves the existing duplicate-item detection: it now runs after the user confirms, so duplicates are merged right before the kit is actually submitted.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Screenshots