test: a token scale of zero decimals is used, not skipped (closes #325)

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

TODO.md

@@ -45,6 +45,17 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-05: A token scale of zero decimals is tested
+  ([#325](https://git.eeqj.de/sneak/AutistMask/issues/325)).
+  `resolveTokenDecimals()` already used a scale of 0 from the bundled list or
+  from a tracked token, but no test said so: turning either of its `d !== null`
+  checks into 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 of those two sources,
+  both where it is resolved and on the approval screen's Amount line. The second
+  half of the issue, one shared `toDecimals()`, had already landed with
+  [#349](https://git.eeqj.de/sneak/AutistMask/issues/349).
+
 - 2026-10-05: The e2e suite waits for a save to land before it closes the popup
   ([#446](https://git.eeqj.de/sneak/AutistMask/issues/446)). The Settings round
   trip switched the theme and the network and closed the popup at once, and a