Implement personal_sign and eth_signTypedData_v4 message signing

Replace stub error handlers with full approval flow for personal_sign,
eth_sign, eth_signTypedData_v4, and eth_signTypedData. Uses toolbar
popup only (no fallback window) and keeps sign approvals pending across
popup close/reopen cycles so the user can respond via the toolbar icon.

src/popup/views/helpers.js

@@ -26,6 +26,7 @@ const VIEWS = [
     "transaction",
     "approve-site",
     "approve-tx",
+    "approve-sign",
 ];
 
 function $(id) {