The non-Mk2 sheet had two inputs named system.details.credits (header
+ finances tab). Foundry concatenates duplicate names as "500,500"
which is not a valid number, causing the field to show blank/grey
after saving.
Fix: finances tab input made readonly with no name attribute — header
is now the sole authoritative credits field.
Also: on-boot sanitization now covers credits, fixing any actors
already storing the corrupted comma-string value.