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

backend/script/lint

@@ -1,50 +1,13 @@
 #!/bin/sh
-# script/lint: run golangci-lint over the backend. This runs inside the
-# lint stage of the root Dockerfile, whose digest-pinned golangci-lint
-# image provides the linter; nothing installs golangci-lint on the host.
-# From a checkout, run `make lint` at the repo root, which builds that
-# stage.
-#
-# .golangci.yml is standardized org-wide and must never be edited here
-# (REPO_POLICIES.md). Its last silent drift replaced the v2 schema with
-# v1 keys, which left every threshold in the file inert while the build
-# stayed green. So the file is first checked against the canonical
-# copy's sha256: a local comparison, no network, nothing unpinned.
+# script/lint: lint the whole repo as the root make lint does, by
+# building the lint phase of the root Dockerfile. golangci-lint never
+# runs on the host (REPO_POLICIES.md).
 set -eu
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
-
-# The sha256 of the org standard .golangci.yml. When that file changes in
-# sneak/prompts and is copied here again, this changes with it.
-GOLANGCI_CONFIG_SHA256="a79b63a254602a5318db5d0e9a06bc71b84bf0c1d896305229d8bfed1d1b1776"
+ROOT="$(cd "$(dirname "$0")/../.." && pwd -P)"
 
 main() {
-    cd "$ROOT"
-    if [ ! -f .golangci.yml ]; then
-        echo "backend/.golangci.yml is missing. Copy the org standard verbatim" >&2
-        echo "from https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml" >&2
-        exit 1
-    fi
-    actual="$(sha256sum .golangci.yml | cut -d' ' -f1)"
-    if [ -z "$actual" ]; then
-        echo "sha256sum is missing or printed no hash, so" >&2
-        echo "backend/.golangci.yml could not be checked." >&2
-        exit 1
-    fi
-    if [ "$actual" != "$GOLANGCI_CONFIG_SHA256" ]; then
-        echo "backend/.golangci.yml does not match GOLANGCI_CONFIG_SHA256" >&2
-        echo "in backend/script/lint." >&2
-        echo "  expected $GOLANGCI_CONFIG_SHA256" >&2
-        echo "  actual   $actual" >&2
-        echo "Compare it with the org standard," >&2
-        echo "https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml" >&2
-        echo "- If they differ, it was edited here: restore the org standard" >&2
-        echo "  verbatim. Do not edit it." >&2
-        echo "- If they are the same, the org standard changed: set" >&2
-        echo "  GOLANGCI_CONFIG_SHA256 in backend/script/lint to the actual hash." >&2
-        exit 1
-    fi
-    golangci-lint run ./...
+    exec "$ROOT/script/lint"
 }
 
 main "$@"