persist confirm-tx view across popup close/reopen (closes #77)

Add confirm-tx to RESTORABLE_VIEWS and save pendingTx in
state.viewData so the confirmation screen survives the popup
lifecycle. On restore, re-render the full confirmation view
including gas estimate.

src/popup/views/confirmTx.js

@@ -39,6 +39,13 @@ const EXT_ICON =
 
 let pendingTx = null;
 
+function restore() {
+    const d = state.viewData;
+    if (d && d.pendingTx) {
+        show(d.pendingTx);
+    }
+}
+
 function etherscanTokenLink(address) {
     return `https://etherscan.io/token/${address}`;
 }
@@ -229,6 +236,7 @@ function show(txInfo) {
     // Gas estimate — show placeholder then fetch async
     $("confirm-fee").classList.remove("hidden");
     $("confirm-fee-amount").textContent = "Estimating...";
+    state.viewData = { pendingTx: txInfo };
     showView("confirm-tx");
 
     estimateGas(txInfo);
@@ -359,4 +367,4 @@ function init(ctx) {
     });
 }
 
-module.exports = { init, show };
+module.exports = { init, show, restore };