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

ConfirmTx and the wait, success and error screens printed the text from
Send's amount field as typed or as Max filled it in: `0.5 ETH`, `.5 ETH`, or
`1.234147890123456789 ETH` after Max, where TxApproval shows a site's send
as `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(). It hands the status screens a copy carrying
that text. The transaction is still signed for the exact amount, which stays
on the pending transaction, and the USD value is priced from it. 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),
     );