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 the golangci-lint
v2.14.0 image, which also runs the js-lint stage, and Dockerfile.lint is
gone. Tests move into a test phase on the golang bookworm 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 The workflow no longer calls script/ci-mark-superseded, so it and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/docker

@@ -1,10 +1,8 @@
 #!/bin/sh
 # script/docker: build the Docker image tagged with the project name.
-# The tag comes from script/projectname.
-#
-# The version script/version resolves here goes in as the VERSION build
-# arg, which takes precedence over what the build would derive from the
-# .git in its context.
+# Identical in all repos; the tag comes from script/projectname.
+# --no-cache because the gate phases the final stage depends on are RUN
+# steps, and a cached one is a check that did not run.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -12,8 +10,14 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build \
-        --build-arg VERSION="$("$SCRIPT_DIR/version")" \
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. The VERSION build argument takes precedence over
+    # the version a build stage derives from the .git in the context.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
         -t "$("$SCRIPT_DIR/projectname")" .
 }