chore: re-vendor canonical files from prompts at dd4027b (closes #472)

Copies .dockerignore, .gitignore, .prettierignore, check.yml and
REPO_POLICIES.md from sneak/prompts at dd4027b. The repo's own entries
(dist/, release/, yarn files) are kept after the canonical content.

The Dockerfile gets separate lint and test phases. Its last stage
depends on both, checks the git describe version and runs make build.
script/lint, test, check, cibuild and docker are the canonical models.
check-censored moves into the lint phase and test-verify-build into the
test phase. fmt and fmt-check fall back to the nvm-installed node. The
e2e image builds are uncached. Comments that cited the old 20-second
test cap now say 60.

Model: opus-5-5

tests/balanceLineEscaping.test.js

@@ -5,7 +5,7 @@
 //
 // The browser half of the same claim — that a real Chrome renders that
 // string as text and puts no iframe in the popup DOM — is in
-// tests/e2e/run.js. This half runs inside the 20-second make test cap.
+// tests/e2e/run.js. This half runs inside the 60-second make test cap.
 
 "use strict";