chore: the native token's label follows the network (closes #372)

networks.js gives each network a nativeCurrency (ETH, SepoliaETH) and nothing
read it: every screen wrote ETH. The wallet's balances and the Send and
confirmation screens now use the active network's. A transaction's figures use
the network its chain id names, through nativeCurrencyByChainId(): the
approval value and fee, the wait, success and error screens, history entries,
the detail screen and the fee-limit refusal, so a site switching networks
cannot make one read as another network's coin. The "ETH" that selectedToken
and txInfo.token hold is the native token's id and is unchanged. A token
reporting any network's nativeCurrency is a spoof, and the detail screen calls
an entry a token transfer when it has a token contract.

Model: opus-5-5

src/popup/views/helpers.js

@@ -267,16 +267,31 @@ function unknownableAmount(balance) {
     return Number.isFinite(n) ? n : null;
 }
 
+// The active network's native token symbol, `ETH` on mainnet and `SepoliaETH`
+// on Sepolia, as src/shared/networks.js names it. The wallet's balances and
+// the Send and confirmation screens, which send on the active network, label a
+// native amount with this; a transaction already made or requested is labelled
+// by its own chain id, through nativeCurrencyByChainId() in networks.js. The
+// "ETH" that state.selectedToken and txInfo.token hold is the native token's
+// id, not its label, and stays "ETH" on every network.
+function nativeCurrency() {
+    return currentNetwork().nativeCurrency;
+}
+
 // A network fee in wei as the confirmation and approval screens both show it:
-// the ETH figure through truncateAmountNeverZero(), then its USD value when the
-// ETH price is known. The USD value is of the exact fee, not of the truncated
-// figure.
-function formatFee(wei) {
+// the ETH figure through truncateAmountNeverZero() and labelled `symbol`, the
+// native currency of the network the fee is paid on, then its USD value when
+// the ETH price is known. The USD value is of the exact fee, not of the
+// truncated figure.
+function formatFee(wei, symbol) {
     const eth = formatEther(wei);
     const ethPrice = getPrice("ETH");
     const usd = ethPrice ? formatUsd(parseFloat(eth) * ethPrice) : "";
     return (
-        truncateAmountNeverZero(eth) + " ETH" + (usd ? " (" + usd + ")" : "")
+        truncateAmountNeverZero(eth) +
+        " " +
+        symbol +
+        (usd ? " (" + usd + ")" : "")
     );
 }
 
@@ -318,7 +333,7 @@ function balanceLine(symbol, amount, price, tokenId) {
 
 function balanceLinesForAddress(addr, trackedTokens, showZero) {
     let html = balanceLine(
-        "ETH",
+        nativeCurrency(),
         parseFloat(addr.balance || "0"),
         getPrice("ETH"),
         "ETH",
@@ -675,6 +690,7 @@ module.exports = {
     balanceLinesForAddress,
     addressHoldsFunds,
     unknownableAmount,
+    nativeCurrency,
     formatFee,
     addressColor,
     addressDotHtml,