fix: a confirmation screen drawn again keeps the network it was reviewed for (closes #586)

ConfirmTx set the transaction's chain id to the active network's every
time it drew the screen, so a popup reopened onto a saved confirmation
after a network switch in Settings described the reviewed transfer as
the new network's and sent it there.

show() now sets the chain id only on a transaction Send hands over, and
the screen describes the transaction entirely on that network: native
currency, USD values, explorer links, and the node and explorer its
checks ask. explorerUrl(), renderAddressHtml(), getPrice(), formatFee()
and checkEtherscanLabel() take an optional chain id for this. A saved
transaction whose chain id names no network is not restored.

Model: opus-5-5

src/shared/prices.js

@@ -2,6 +2,7 @@
 
 const { getTopTokenPrices } = require("./tokenList");
 const { isBelowOneMillionth } = require("./amountDisplay");
+const { networkByChainId } = require("./networks");
 
 const PRICE_CACHE_TTL = 300000; // 5 minutes
 
@@ -36,10 +37,12 @@ function clearPrices() {
     lastFetchedAt = 0;
 }
 
-// Return the USD price for a symbol, or null on testnet / unknown.
-function getPrice(symbol) {
+// Return the USD price for a symbol on the network with `chainId`, or on the
+// active network when no chain id is given; null on testnet / unknown.
+function getPrice(symbol, chainId) {
     const { currentNetwork } = require("./state");
-    if (currentNetwork().isTestnet) return null;
+    const network = chainId ? networkByChainId(chainId) : currentNetwork();
+    if (network.isTestnet) return null;
     return prices[symbol] || null;
 }