fix: the wallet's own send shows its amount to four decimal places (closes #522)

ConfirmTx and the wait, success and error screens printed Send's amount field
as it stood (`.5 ETH`, or every digit Max filled in); TxApproval shows
`0.5000 ETH`. ConfirmTx now writes the amount as TxApproval does: parsed at the
scale it is encoded with, written back as plain decimal text and cut by
truncateAmountNeverZero(), and hands the status screens a copy carrying that
text. A token whose scale is unknown, which cannot be sent, has the field's
text cut the same way. The transaction is still signed for the exact amount,
which also prices the USD value. A saved confirmation screen whose amount is
not text is no longer redrawn.

Model: opus-5-5

tests/e2e/run.js

@@ -2915,9 +2915,10 @@ async function goToTokenConfirm(env) {
         amount: TOKEN_AMOUNT,
     });
     await waitForEstimate(env.page);
+    // TOKEN_AMOUNT to four decimal places (README.md, Display Consistency).
     const shown = await shownAmount(env.page);
     assert(
-        shown === TOKEN_AMOUNT + " " + STUB_TOKEN.symbol,
+        shown === "0.2500 " + STUB_TOKEN.symbol,
         "the confirmation screen is not showing the amount that was entered: " +
             JSON.stringify(shown),
     );