Fetch real ETH balances from RPC on popup open

Uses ethers JsonRpcProvider to call eth_getBalance for every
address on popup open. Balances update in the background and
re-render the wallet list when done. Default RPC is
eth.llamarpc.com, configurable in settings.

src/popup/index.js

@@ -1,5 +1,11 @@
 // AutistMask popup UI — view management and event wiring
-const { Mnemonic, HDNodeWallet, Wallet } = require("ethers");
+const {
+    Mnemonic,
+    HDNodeWallet,
+    Wallet,
+    JsonRpcProvider,
+    formatEther,
+} = require("ethers");
 
 const DEBUG = true;
 const DEBUG_MNEMONIC =
@@ -113,6 +119,41 @@ function addressFromPrivateKey(key) {
     return w.address;
 }
 
+// -- balance fetching --
+function getProvider() {
+    return new JsonRpcProvider(state.rpcUrl);
+}
+
+function formatBalance(wei) {
+    const eth = formatEther(wei);
+    // Show up to 6 decimal places, trim trailing zeros
+    const parts = eth.split(".");
+    if (parts.length === 1) return eth + ".0";
+    const dec = parts[1].slice(0, 6).replace(/0+$/, "") || "0";
+    return parts[0] + "." + dec;
+}
+
+async function refreshBalances() {
+    const provider = getProvider();
+    const updates = [];
+    for (const wallet of state.wallets) {
+        for (const addr of wallet.addresses) {
+            updates.push(
+                provider
+                    .getBalance(addr.address)
+                    .then((bal) => {
+                        addr.balance = formatBalance(bal);
+                    })
+                    .catch(() => {
+                        // leave balance unchanged on error
+                    }),
+            );
+        }
+    }
+    await Promise.all(updates);
+    await saveState();
+}
+
 // -- render wallet list on main view --
 function renderWalletList() {
     const container = $("wallet-list");
@@ -268,6 +309,10 @@ async function init() {
     } else {
         renderWalletList();
         showView("main");
+        // Fetch balances in the background, re-render when done
+        refreshBalances().then(() => {
+            renderWalletList();
+        });
     }
 
     // -- Welcome --