Re-vendor the shared files from sneak/prompts at dd4027b (closes #113)

The shared files are the sneak/prompts copies at dd4027b, with this
repository's own entries after them. make lint and make test each build
one Dockerfile phase without the cache, both covering the frontend
through a node stage; the builder stage waits on both and takes its
version from git describe unless VERSION is given. golangci-lint moves
to v2.14.0 with the new .golangci.yml; one test spells X-Request-ID as
canonicalheader asks. prettier formats only JavaScript, CSS, HTML and
Markdown, so .golangci.yml stays as fetched. script/fmt and
script/fmt-check put ~/.local/bin on PATH, which the shared workflow no
longer does. script/bootstrap keeps a Go only if it is exactly
GO_VERSION, and re-checks the go on PATH after installing.

Model: opus-5-5

script/lint

@@ -1,23 +1,23 @@
 #!/bin/sh
-# script/lint: lint the whole repo: eslint over the frontend, then the Go
-# linter over backend/.
+# 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.
 #
-# No linter runs on the host: this builds the frontend-lint and lint
-# stages of Dockerfile, the digest-pinned node and golangci-lint images.
-# The first runs eslint; the second runs the backend's fmt-check and
-# lint targets. --no-cache makes each linter really run every time
-# rather than reuse an earlier result, and each stage is built for its
-# checks alone, so no image is kept.
+# 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 "$ROOT"
-    timeout 300 docker build --no-cache --target frontend-lint \
-        --output type=cacheonly .
-    timeout 300 docker build --no-cache --target lint \
-        --output type=cacheonly .
+    docker build --no-cache \
+        --target lint \
+        -t "$("$SCRIPT_DIR/projectname")-lint" .
 }
 
 main "$@"