Re-vendor the shared files from sneak/prompts at dd4027b (closes #504)

Fetches the shared files unchanged from sneak/prompts commit dd4027b and
adds .prettierignore; .dockerignore keeps this repository's anchored host
artifacts at its end.

Linting moves into the Dockerfile's lint phase on golangci-lint v2.14.0,
which also runs ESLint, and Dockerfile.lint is gone. Tests move into a test
phase on the Debian Go image. script/lint, test, docker and cibuild are the
model scripts, every docker build in script/ passes --no-cache, and the
.ci-fingerprint barrier is gone. The workflow no longer calls
script/ci-mark-superseded, so it and its tests are removed. make build
passes -trimpath and -s -w.

Model: opus-5-5

script/version

@@ -1,9 +1,11 @@
 #!/bin/sh
 # script/version: output the version string the binary is stamped with.
 # Our own extension to scripts-to-rule-them-all. The Makefile's build
-# target and script/docker both take the value from here, so a `make
-# build` binary and a `make docker` image built from the same checkout
-# report the same thing.
+# and version targets take the value from here, and the Dockerfile's
+# build stage calls them. script/docker and script/cibuild run the same
+# `git describe` on the host and pass the result in as $VERSION, so a
+# `make build` binary and a `make docker` image built from the same
+# checkout report the same thing.
 #
 # Order of precedence:
 #