fix: TxApproval prices a site's ETH send from its exact amount on its own network (closes #614)

TxApproval worked out the USD value of a site's ETH send from the
four-decimal figure it shows, at the price on the active network, so the
same value read a few cents different than on ConfirmTx, and a
transaction on another network was priced at the active one's rate, its
network fee too. It now prices the exact value with getPrice("ETH",
chainId) for the transaction's chain id, as ConfirmTx does, and passes
that chain id to formatFee() for the fee.

getPrice() now returns null for a chain id that names no network instead
of throwing, so such a transaction is still shown, with no USD value.

Model: opus-5-5

src/popup/views/approval.js

@@ -231,10 +231,11 @@ function showTxFee(approvedTx) {
     const feePerGas = BigInt(approvedTx.maxFeePerGas || approvedTx.gasPrice);
     // Through formatFee(), as the confirmation screen's fee is, so the same
     // fee reads the same on both. In the native currency of the network shown
-    // above, as the value is.
+    // above, and at the price on it, as the value is.
     $("approve-tx-fee").textContent = formatFee(
         gasLimit * feePerGas,
         nativeCurrencyByChainId(approvedTx.chainId),
+        approvedTx.chainId,
     );
 
     let detail =
@@ -367,11 +368,12 @@ function showTxApproval(details) {
         $("approve-tx-to").innerHTML = escapeHtml(CONTRACT_CREATION_TEXT);
     }
 
-    const ethValueFormatted = formatTxValue(
-        formatEther(approvedTx.value || "0"),
-    );
-    const ethPrice = getPrice("ETH");
-    const ethUsd = ethPrice ? parseFloat(ethValueFormatted) * ethPrice : null;
+    const ethValueFormatted = formatTxValue(ethValue);
+    // Priced from the exact value, not the four-decimal figure, at the price
+    // on the network the transaction is for, as the confirmation screen prices
+    // its amount, so the same value reads the same on both.
+    const ethPrice = getPrice("ETH", approvedTx.chainId);
+    const ethUsd = ethPrice ? parseFloat(ethValue) * ethPrice : null;
     const usdStr = formatUsd(ethUsd);
     // In the native currency of the network the transaction is for, which the
     // Network line names, not the active network's: the active network can