Enhance confirm transaction page with full verification details

The confirmation page now shows:
- Transaction type (Native ETH transfer vs ERC-20 token transfer)
- Full ERC-20 token contract address with etherscan link
- Token symbol throughout (not raw contract address)
- Current balance of the token being sent, with USD value
- Estimated network fee in ETH and USD (fetched async)
- USD value for ERC-20 token amounts (not just ETH)
- Insufficient balance errors for ERC-20 tokens

Also implements actual ERC-20 token transfers via the token contract's
transfer() function, rather than only supporting native ETH sends.

src/popup/views/send.js

@@ -92,6 +92,16 @@ function init(_ctx) {
         const token = state.selectedToken || $("send-token").value;
         const addr = currentAddress();
 
+        let tokenSymbol = null;
+        let tokenBalance = null;
+        if (token !== "ETH") {
+            const tb = (addr.tokenBalances || []).find(
+                (t) => t.address.toLowerCase() === token.toLowerCase(),
+            );
+            tokenSymbol = tb ? tb.symbol : "?";
+            tokenBalance = tb ? tb.balance || "0" : "0";
+        }
+
         ctx.showConfirmTx({
             from: addr.address,
             to: resolvedTo,
@@ -99,6 +109,8 @@ function init(_ctx) {
             amount: amount,
             token: token,
             balance: addr.balance,
+            tokenSymbol: tokenSymbol,
+            tokenBalance: tokenBalance,
         });
     });