When admin clicks 'Start a design for this' on a photo request, now routes
to the design canvas at /made-to-order/{productSlug} with the custom photo
passed as a query parameter. The DesignCanvas component now accepts and
displays the custom photo as the background for designing.
Changes:
- Updated photo request link to go to design canvas page
- Added customPhoto query parameter to pass custom image URL
- Updated DesignCanvas to accept and use customPhoto prop
- Modified renderPhoto() to display custom photo when provided
- Updated getPhotoInfo() to use custom photo for compositing