In this change, instead of *always* inferring the Dyeworks base item
from the item name at runtime, we now have a database field that tracks
it, and auto-populates whenever an item *seems* to need a Dyeworks base
item but doesn't have one yet.
This will enable us to set the base item manually in cases where it
can't be inferred, and load Dyeworks base items for the Item Getting
Guide in one query with `includes(:dyeworks_base_item)`.
This migration does a bit more of the fix-em-up scripting work *in* the
migration itself than I usually do, mainly because there's so much in
this one that I think being extra-explicit is useful. We make sure to
do it gracefully though!
Emi Matchu
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