docs: codify merge proof standard (#84)

README.md

@@ -54,6 +54,15 @@ pip install huey
 huey_consumer.py tasks.huey -w 2 -k thread
 ```
 
+## Proof Standard
+
+This repo uses a hard proof rule for merges.
+
+- visual changes require screenshot proof
+- CLI/verifiable changes must cite logs, command output, or world-state proof
+- screenshots/media stay out of Gitea backup unless explicitly required
+- see `CONTRIBUTING.md` for the merge gate
+
 ## Deploy
 
 ```bash