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/test-verify-build

@@ -2,7 +2,8 @@
 # script/test-verify-build: exercise every failure mode of
 # script/verify-build, and what make build does with dist/ after one of them
 # (script/discard-dist-on-failure). Our own extension to
-# scripts-to-rule-them-all, run from script/check so make check covers it.
+# scripts-to-rule-them-all, run by the Dockerfile's test phase so make check
+# covers it.
 #
 # Why this exists: verify-build is the build-integrity guard, and four separate
 # reviews of it each found a fresh vacuous pass — the grep exit-2 conflation,