Move Go overlay to plugin/languages/go/ (#13)

* Move Go plugin overlay from languages/go/ to plugin/languages/go/

Aligns Go with the Java/Python/JavaScript convention where all language
overlays live under plugin/languages/<lang>/. The Makefile already
discovers from plugin/languages/* so Go is now included in builds.

* Remove accidental read-tracker changes

* Ignore .codeflash/observability/ in gitignore

.gitignore

@@ -7,6 +7,7 @@ __pycache__/
 original_base_research/
 .claude/settings.local.json
 .claude/handoffs/
+.codeflash/observability/
 dist/
 dist-*/
 dist-v2/