chore: add changeset for manifest version automation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ryanbas21

.changeset/manifest-version-automation.md

@@ -0,0 +1,7 @@
+---
+'@wolfcola/devtools-extension': patch
+---
+
+Automate manifest version stamping: append CI build number as 4th version
+segment so every Chrome Web Store and Firefox Add-ons upload has a unique,
+always-increasing version.