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/frontend-fmt

@@ -1,6 +1,8 @@
 #!/bin/sh
-# script/frontend-fmt: format the frontend and every other file prettier
-# understands, repo-wide (writes), the markdown in backend/ included.
+# script/frontend-fmt: format the JavaScript, CSS, HTML and Markdown,
+# repo-wide (writes), the markdown in backend/ included. Those are the
+# languages REPO_POLICIES.md gives prettier; the YAML is left alone, as
+# backend/.golangci.yml must stay the org standard byte for byte.
 # Prettier does not read Go; backend/script/fmt formats the Go sources.
 set -eu
 
@@ -8,7 +10,7 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    yarn prettier --write .
+    yarn prettier --write '**/*.{js,css,html,md}'
 }
 
 main "$@"