Release/1.39.0-rc.4 (#2797)

* chore: bump version to 1.39.0 for release

* chore: bump to 1.39.0-rc.1

* chore: bump to 1.39.0-rc.2

* chore: bump to 1.39.0-rc.3

* chore: bump to 1.39.0-rc.4

* docs: add v1.39.0-rc.4 release notes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

sdk/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@gsd-build/sdk",
-  "version": "0.1.0",
+  "version": "1.39.0-rc.4",
   "description": "GSD SDK — programmatic interface for running GSD plans via the Agent SDK",
   "type": "module",
   "main": "dist/index.js",