Fix: Correct Response Handling in ClientSend

[GODrums]

Bug

Most of our enhanced pages currently print these errors:

EmptyResponseHandler returns void after successful execution, causing ClientSend to reject the promise.
Addresses errors mentioned in #402 as well

Fix

Only reject on error, otherwise resolve with undefined. Functionality unchanged, just gets rid of an incorrect rejection.

---

< />!NOTE< />
Low Risk
Single-branch change in bridge client response handling; aligns with how the background already sends success vs error bundles.

Overview
Fixes incorrect promise rejection in ClientSend when talking to the background worker via runtime.sendMessage.

The callback now rejects only when resp.error is set and resolves with resp.response otherwise (including undefined). Previously, a missing/falsy response was treated as failure, so handlers like EmptyResponseHandler that complete successfully with no payload caused spurious rejections and console errors on enhanced pages.

Reviewed by Cursor Bugbot for commit 712400b. Configure here.