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 test caps
now say 60 seconds, and comments that named what runs a script now name
the Dockerfile phase or stage.

Model: opus-5-5

script/lint

@@ -1,51 +1,23 @@
 #!/bin/sh
-# script/lint: run the linter (eslint, then prettier --check).
+# script/lint: run the linter. Linting is a phase of the Dockerfile and
+# this builds that phase alone; the linter is never installed or run on
+# a developer host, where a shared result cache and a host-global lock
+# make its answer untrustworthy.
 #
-# Linting is containerized. ESLint results depend on the ESLint version, and
-# the pinned one is the one in the image; a host's own install must not be
-# able to decide whether this repo is green. From a host this therefore builds
-# the Dockerfile's `lint` stage, which runs this same script inside the image.
-#
-# AUTISTMASK_LINT_NATIVE is set only in that image (see the Dockerfile) and is
-# what stops the recursion, so `make check` inside the CI build lints in place
-# instead of trying to reach a docker daemon it does not have.
+# The phase is not the last stage in the file, so it is built only when
+# --target names it. --no-cache because a cached lint layer is a lint
+# that did not run. The tag makes each build replace the previous image
+# instead of leaving a dangling one behind.
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-
-    case "${AUTISTMASK_LINT_NATIVE:-}" in
-    1)
-        echo "Linting..."
-        yarn run lint 2>&1
-        return 0
-        ;;
-    "") ;;
-    *)
-        # Set but not recognized: say so rather than silently taking the
-        # docker path, which would look like the variable had no effect.
-        echo "lint: AUTISTMASK_LINT_NATIVE is set to" \
-            "'${AUTISTMASK_LINT_NATIVE}'; the only recognized value is 1" >&2
-        exit 1
-        ;;
-    esac
-
-    if ! command -v docker >/dev/null 2>&1; then
-        echo "lint: docker is required; linting does not run on the host" >&2
-        exit 1
-    fi
-
-    echo "Linting in the pinned container..."
-    # --progress=plain: the default progress renderer collapses the lint
-    # output on success, and a lint run whose output cannot be seen is not
-    # evidence that it ran.
-    #
-    # --output=type=cacheonly: the exit status is the whole result; exporting
-    # an image afterwards costs about ten times the lint itself.
-    docker build --progress=plain --target lint \
-        --output=type=cacheonly . 2>&1
+    docker build --no-cache \
+        --target lint \
+        -t "$("$SCRIPT_DIR/projectname")-lint" .
 }
 
 main "$@"