feat(send): show fee + total on the compose form; fix the stuck confirm on recheck

- The network fee and running total are now shown on the compose form (once an
  amount is entered), instead of only being revealed in the confirm popup.
- When the pre-broadcast re-validation fails (balance dropped, sync restarted,
  fee pushed total over available), the confirm popup now closes and surfaces a
  warning toast — previously the reason was drawn on the form behind the still-
  open popup, so the user was left re-clicking a button that did nothing.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -2550,6 +2550,8 @@ void I18n::loadBuiltinEnglish()
         strings_["send_go_to_receive"] = "Go to Receive";
         strings_["send_keep"] = "Keep";
         strings_["send_network_fee"] = "NETWORK FEE";
+        strings_["send_network_fee_label"] = "Network fee:";
+        strings_["send_total_label"] = "Total:";
         strings_["send_no_balance"] = "No balance";
         strings_["send_no_recent"] = "No recent sends";
         strings_["send_recent_sends"] = "RECENT SENDS";