Add test requirements to checklists, .dockerignore URLs, root symlink, and Makefile comment

- Add test requirement item to both checklists (must not be a no-op)
- Add .dockerignore template URL to Dockerfile items in both checklists
- Add REPO_POLICIES.md symlink in repo root pointing to prompts/
- Add comment to Makefile explaining why prettier flags are repeated

REPO_POLICIES.md

@@ -0,0 +1 @@
+prompts/REPO_POLICIES.md