Restructure sidebar: Make B2C drop-ins visible at same level as B2B

- Moved B2C drop-ins from nested subsection to top-level section
- Now matches B2B drop-ins structure
- Makes all 10 B2C drop-ins easily discoverable
- Previous structure had B2C drop-ins hidden inside 'Drop-ins' overview section

Structure now:
- Drop-ins (overview and general info)
- B2C Drop-ins (Cart, Checkout, Order, etc.)
- B2B Drop-ins (Company Management, Purchase Order, etc.)

Author: bdenham