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

test/viewport/README.md

@@ -13,8 +13,8 @@ width derived from the app's own CSS. Screenshots land in `tmp/viewport/`
 alongside a `results.json`; they are artifacts for a human to look at when
 something fails, not the evidence. The assertions are the evidence.
 
-The target is deliberately outside `make check`: it needs Docker and takes
-minutes, and `make test` has to stay under 20 seconds.
+The target is deliberately outside `make check`: it takes minutes, and
+`make test` has to stay under 60 seconds.
 
 ## How the widths are chosen