fix: only the user switches the wallet's network (closes #408)

A connected site's wallet_switchEthereumChain request for the other
supported network now opens a prompt in its own window, through the
existing approval machinery, naming the site and both networks. The
network, endpoints, balances and caches change, and chainChanged is
sent, only when the user approves it; rejecting or closing the prompt
answers 4001. One such prompt per site at a time; a request for the
active network needs none. The approval window no longer shows the
connection prompt while it waits for the approval's description,
since both prompts answer on the same port.

Model: opus-5-5

src/popup/views/transactionDetail.js

@@ -84,8 +84,9 @@ function show(tx) {
             contractAddress: tx.contractAddress || null,
             // The network the history entry was read from. The type line and
             // the fee are in its native currency, not the active network's:
-            // a site can switch the active network before a later popup
-            // shows this screen again.
+            // the active network can change, in Settings or when the user
+            // approves a site's request, before a later popup shows this
+            // screen again.
             chainId: tx.chainId,
         },
     };