Show tx status screens after dApp transaction approval

Previously the approval popup closed immediately after the user
entered their password, giving zero feedback about whether the
transaction was broadcast or confirmed. Now:

1. Background sends the broadcast result back to the popup via
   sendResponse callback (txHash or error)
2. Popup shows wait-tx screen on success (with polling timer)
   or error-tx screen on failure
3. Wait-tx polls for confirmation and transitions to success-tx
4. Done button closes the approval window

txStatus.init() moved before the approval early-return so the
wait/success/error views are wired up in the approval popup.
Done buttons detect the approval context and call window.close()
instead of navigating to address detail.

src/popup/views/txStatus.js

@@ -161,7 +161,15 @@ function renderError() {
     showView("error-tx");
 }
 
+function isApprovalPopup() {
+    return new URLSearchParams(window.location.search).has("approval");
+}
+
 function navigateBack() {
+    if (isApprovalPopup()) {
+        window.close();
+        return;
+    }
     if (state.selectedToken) {
         ctx.showAddressToken();
     } else {