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

@@ -1,14 +1,14 @@
 #!/bin/sh
-# script/check: run all checks (test, test-verify-build, lint, fmt-check).
-# Our own extension to scripts-to-rule-them-all. Must not modify any files.
+# script/check: run all checks (test, lint, fmt-check). Our own
+# extension to scripts-to-rule-them-all. test and lint are Docker
+# phases; fmt-check is native, because a formatter writes the working
+# tree. Must not modify any files.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
 
 main() {
     "$SCRIPT_DIR/test"
-    "$SCRIPT_DIR/test-verify-build"
-    "$SCRIPT_DIR/check-censored"
     "$SCRIPT_DIR/lint"
     "$SCRIPT_DIR/fmt-check"
 }