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, keeping the repo's own
entries (dist/, release/, yarn files) 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 citing the old test caps or what
runs a script are updated.

Model: opus-5-5

script/check-censored

@@ -1,8 +1,8 @@
 #!/bin/sh
 # script/check-censored: assert that the competitor name RULES.md bars appears
 # nowhere in this repo, and nowhere in the built extension, except where it is
-# deliberate. Our own extension to scripts-to-rule-them-all, run from
-# script/check and from make build.
+# deliberate. Our own extension to scripts-to-rule-them-all, run by the
+# Dockerfile's lint phase and by make build.
 #
 # Where the name is allowed, and why each one is not negotiable away:
 #