chore(node-core): Deprecate @sentry/node-core package (#22285)

The `@sentry/node-core` SDK is being merged back into `@sentry/node` in
the next major version. Add a deprecation notice to the README ahead of
removal.

Closes
https://linear.app/getsentry/issue/SDK-1345/add-deprecation-notice-in-sentrynode-core

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: msonnb

packages/node-core/README.md

@@ -4,7 +4,10 @@
   </a>
 </p>
 
-# Official Sentry SDK for Node-Core
+# Official Sentry SDK for Node-Core (DEPRECATED)
+
+> DEPRECATION NOTICE: The `@sentry/node-core` package is deprecated and will be removed in the next major version.
+> Its functionality will be merged back into the `@sentry/node` SDK.
 
 [![npm version](https://img.shields.io/npm/v/@sentry/node-core.svg)](https://www.npmjs.com/package/@sentry/node-core)
 [![npm dm](https://img.shields.io/npm/dm/@sentry/node-core.svg)](https://www.npmjs.com/package/@sentry/node-core)