fix(utils): tolerate null self in worker runtime detection

typeof null is 'object', so a mocked environment defining self = null passed
the typeof guard and the importScripts access would throw. Optional chaining
degrades it to undefined and falls through to the server checks, matching the
file's existing navigator?.sendBeacon idiom.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: abbaseya

packages/utils/src/http-client.ts

@@ -146,7 +146,7 @@ const determineRuntime = (): RuntimeResult => {
   // endpoint rejected, breaking every signals worker upload).
   if (
     typeof self !== 'undefined' &&
-    typeof (self as {importScripts?: unknown}).importScripts === 'function'
+    typeof (self as {importScripts?: unknown})?.importScripts === 'function'
   ) {
     return {runtime: 'browser'};
   }