feat: scaffold go backend foundation

AGENTS.md

@@ -56,5 +56,13 @@ For planning/spec-only changes, run:
 openspec validate bootstrap-job-tutor-platform --strict
 ```
 
-For future code changes, add project-specific build and test commands here once
-the implementation stack is initialized.
+For Go backend changes, run:
+
+```powershell
+gofmt -w cmd internal
+go test ./...
+openspec validate bootstrap-job-tutor-platform --strict
+```
+
+Before completing implementation work, confirm manually authored Go files stay
+at or below 600 lines.