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

The shared files are the sneak/prompts copies at dd4027b, plus this
repository's own entries. make lint and make test each build one
Dockerfile phase without the cache, both covering the frontend; the
builder stage waits on both and takes its version from git describe
unless VERSION is given. The test phase keeps Go's module and build
caches in memory, out of the image make test tags. 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. 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

Makefile

@@ -1,5 +1,5 @@
 .PHONY: bootstrap setup dev build test lint fmt fmt-check check \
-	add-dependency tidy frontend-check frontend-viewport-test docker hooks
+	add-dependency tidy frontend-viewport-test docker hooks
 
 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -42,14 +42,8 @@ add-dependency:
 tidy:
 	@script/tidy
 
-# The frontend tests and format check, for Dockerfile's frontend stage,
-# which has neither Go nor Docker. Use check everywhere else.
-frontend-check:
-	@script/frontend-check
-
 # Responsive-layout verification in a containerised browser. Kept out of
-# check: it needs Docker and takes minutes, where make test has to stay
-# under 20 seconds.
+# check: it takes minutes.
 frontend-viewport-test:
 	@script/frontend-viewport-test