Re-vendor the canonical files from sneak/prompts dd4027b (closes #159, closes #116)

Fetches .dockerignore, .editorconfig, the CI workflow, .gitignore,
.golangci.yml, .prettierignore, .prettierrc and REPO_POLICIES.md byte
for byte from sneak/prompts dd4027b; this repo's own entries follow the
canonical text in .dockerignore, .gitignore and .editorconfig. The new
.golangci.yml disables gomodguard. The Dockerfile gets a lint phase on
golangci-lint v2.14.0 and a test phase on the Debian Go image; the
build stage depends on both and stamps the version as the policy shows.
script/test and script/lint build only their phase, and script/cibuild
bootstraps and runs script/check first. bin/tools goes: script/bootstrap
installs gofumpt and protoc-gen-go into bin/ with go install pinned to a
commit.

Model: opus-5-5

.prettierignore

@@ -1,14 +1,2 @@
-# REPO_POLICIES.md is a verbatim copy of an authoritative upstream
-# document (sneak/prompts). Local tooling must never rewrite it: any
-# reformatting is silent drift from the source of truth.
-REPO_POLICIES.md
-
-# User-owned configuration, copied verbatim from upstream. Not matched by
-# the current prettier file set, but listed so widening that set can never
-# start rewriting it.
-.golangci.yml
-
-# Dependencies and build output
 node_modules/
-vendor/
-bin/
+yarn.lock