Fix layout shift from async USD prices and token balances

Reserve vertical space with min-height and   placeholders for all
elements populated by async data: per-address USD totals, ETH price
display, token balance containers, and total value sub-line.  Prevents
buttons and click targets from moving when price API responds.

src/popup/views/addressToken.js

@@ -124,7 +124,8 @@ function show() {
 
     // USD total for this token only
     const usdVal = price ? amount * price : 0;
-    $("address-token-usd-total").textContent = formatUsd(usdVal);
+    const usdStr = formatUsd(usdVal);
+    $("address-token-usd-total").innerHTML = usdStr || " ";
 
     // Single token balance line (no tokenId — not clickable here)
     $("address-token-balance").innerHTML = balanceLine(symbol, amount, price);