fix: the confirmation screen reads its balance on the network it is drawn for (closes #558)

ConfirmTx showed and checked the balance Send handed it, so a popup reopened onto a confirmation saved before a network switch stated the other network's balance and checked the amount against it.

Each time it is shown, ConfirmTx now reads the From address's ETH balance, and for a token send its token balance, from the node of the network it is drawn for, and gives that node to the fee estimate, which starts once the read is done. Until then the balance line says "Loading..." and Sign & Send stays disabled; a failed read is stated as unknown. Each message the read can bring has a box reserved from the first paint, so nothing moves when it returns.

Model: opus-5-5

tests/sendAmountRule.test.js

@@ -23,7 +23,10 @@ jest.mock("../src/shared/log", () => ({
     isDebug: () => false,
 }));
 
-// What the confirmation screen asks the node for.
+const { AbiCoder } = require("ethers");
+
+// What the confirmation screen asks the node for. The address holds the 1 ETH
+// and 250 TOK the wallet below records.
 const mockProvider = {
     getFeeData: async () => ({
         maxFeePerGas: 2000000000n,
@@ -32,7 +35,11 @@ const mockProvider = {
     estimateGas: async () => 21000n,
     getCode: async () => "0x",
     getTransactionCount: async () => 1,
-    getBalance: async () => 0n,
+    getBalance: async () => 1000000000000000000n,
+    // The one contract call the screen makes, balanceOf(), answered at the
+    // token's 6 decimal places.
+    call: async () =>
+        AbiCoder.defaultAbiCoder().encode(["uint256"], [250000000n]),
 };
 
 jest.mock("../src/shared/balances", () => {