Add a subSortIndex field to inbounds that controls the order of links
in subscription output only: the raw sub body, the HTML sub page, and
the JSON/Clash formats (all served from the same query). Lower values
come first; ties keep id order. The panel inbound list is unaffected.
The value is editable in the inbound form next to the share-address
fields, propagates to nodes via wireInbound, and follows the usual
node-sync rules (copied on import, mirrored while not dirty, never a
structural change).
Rescoped from #5214 by @Ponywka.
f1a4286e2f