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

README.md

@@ -1013,10 +1013,12 @@ rendered differently on two screens.
 
 The native token's label is a network's `nativeCurrency` in
 `src/shared/networks.js`: `ETH` on mainnet, `SepoliaETH` on Sepolia. The
-wallet's balances and the Send and confirmation screens, which send on the
-active network, use the active network's. A transaction's figures use the one of
-the network its chain id names, whichever network is active: the value and fee
-on the approval screen, the amount on the wait, success and error screens, the
+wallet's balances and the Send screen, which sends on the active network, use
+the active network's. The confirmation screen uses the one of the network its
+transaction was reviewed on, the network active when Send showed it, even after
+the network is switched in Settings. A transaction's figures use the one of the
+network its chain id names, whichever network is active: the value and fee on
+the approval screen, the amount on the wait, success and error screens, the
 transaction history and the transaction detail screen, and the refusal of a fee
 above 1 ETH. A chain id that names no network reads `ETH`. Wherever this
 document shows ETH as the label of a native balance, value or fee, in a "Native
@@ -1782,12 +1784,20 @@ view would leave a wallet one click from deletion.
       the contract's own answer is read at signing time only to be compared with
       it, and a disagreement is a refusal rather than a preference for either
       value (`src/shared/transferAmount.js`)
-    - "Sign & Send" after the active network was switched in Settings while this
-      screen was open → nothing is signed; "The active network changed after
+    - "Sign & Send" after the active network was switched in Settings since this
+      transaction was reviewed, with this screen open or before the popup
+      reopened onto it → nothing is signed; "The active network changed after
       this transaction was reviewed, so it was not sent. Please go back and
       review it again." in the errors box, no screen change. The transaction
-      carries the chain id of the network the screen was shown for, so it cannot
-      be signed for another
+      carries the chain id of the network active when Send showed this screen,
+      and keeps it when the screen is drawn again from the saved transaction, so
+      it cannot be signed for another. The screen describes it on that network,
+      whichever network is active: its amounts are in that network's native
+      currency, its USD values are that network's, so a testnet transaction
+      shows none, its From, To and token contract links open that network's
+      explorer, the fee estimate and the contract and never-sent recipient
+      checks ask that network's RPC endpoint, and the Etherscan label check asks
+      that network's explorer
     - "Sign & Send" (wrong password) → "Wrong password." on the password error
       line, no screen change
     - "Sign & Send" signs as the From address above, not as whichever address is