fix(craft): Add missing mainDocsUrl for @sentry/effect SDK

The Effect SDK was missing the mainDocsUrl field in the craft configuration,
causing KeyError: 'main_docs_url' in Sentry backend (SENTRY-5M6R).

This adds the documentation URL following the same pattern as other
JavaScript SDKs in the registry.

Fixes SENTRY-5M6R

Author: bc-sentry

.craft.yml

@@ -244,4 +244,5 @@ targets:
         name: 'Sentry Effect SDK'
         sdkName: 'sentry.javascript.effect'
         packageUrl: 'https://www.npmjs.com/package/@sentry/effect'
+        mainDocsUrl: 'https://docs.sentry.io/platforms/javascript/guides/effect/'
         onlyIfPresent: /^sentry-effect-\d.*\.tgz$/