resolveTokenDecimals() treats a scale of 0 from the bundled list or a
tracked token as an answer, but nothing tested it: changing either
`d !== null` check to a plain truthiness check left every test green
while a zero-decimal token fell through to the next source or to
"decimals unknown".
The approval tests now assert a scale of 0 from each source, both from
the resolver and on the approval screen's Amount line. toDecimals() was
already shared from transferAmount.js since #349.
Model: opus-5-5
sneak