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/fmt

@@ -1,6 +1,6 @@
 #!/bin/sh
-# script/fmt: format the whole repo (writes): prettier over everything
-# it understands, then gofmt over the Go backend.
+# script/fmt: format the whole repo (writes): prettier over the
+# JavaScript, CSS, HTML and Markdown, then gofmt over the Go backend.
 # The org model formats only markdown; this repo also has JS and Go.
 set -eu
 
@@ -8,6 +8,9 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
+    # script/bootstrap links the node, yarn and gofmt it installs into
+    # ~/.local/bin, which the shell that called it may not have on PATH.
+    PATH="$HOME/.local/bin:$PATH"
     "$ROOT/script/frontend-fmt"
     "$ROOT/backend/script/fmt"
 }