Includes the associated Go functions for inserting and selecting given a
specific user ID or subscription ID. Also adds required HTML tags and
HTTP queries for subscription process during user registration.

Also structure CLI functions to allow for `skouter dev seed` command.

Uses gift package for server side resizing of selected letterhead
file. It should fit an image file with aspect ratio of 2:1 and be a
reasonable size. A 400x200 resizeToFit is used for now.
gift just uses the native image/draw package internally.
https://pkg.go.dev/image/draw

Setup structs for storing query information.