Registers an already-uploaded blank PDF as a form template. The browser uploads straight to
Supabase, so the key is untrusted: it must sit under the caller's own prefix, and the bytes must
be a PDF the fill engine can use. Both checks run BEFORE the insert, so a rejection needs no
compensating delete. No resource middleware: like list, there is no existing form to authorize.
Registers an already-uploaded blank PDF as a form template. The browser uploads straight to Supabase, so the key is untrusted: it must sit under the caller's own prefix, and the bytes must be a PDF the fill engine can use. Both checks run BEFORE the insert, so a rejection needs no compensating delete. No resource middleware: like
list, there is no existing form to authorize.