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, keeping this repo's anchored
host-built artifacts in .dockerignore; 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,
and bin/.gitignore ignores what lands in bin/.

Model: opus-5-5

.dockerignore

@@ -17,7 +17,17 @@
 # stage that compiles runs `git describe --tags --always` on .git, which
 # does not need .git/config; that file can hold a credential, such as a
 # password in a remote URL or the token the CI checkout step stores there.
-.git/config
+# Each submodule keeps a config with the same exposure in its git directory
+# under .git/modules/, nested again for a submodule's own submodules, or in
+# its own .git directory when it keeps one.
+# KNOWN GAP: a submodule whose name has a `config` segment (`config`,
+# `deploy/config`, `config/lib`) loses its whole git directory, because
+# `**/.git/modules/**/config` also matches that segment's directory
+# under .git/modules/. Go's version stamping then fails the build;
+# nothing leaks. Name such a submodule without that segment:
+# `git submodule add --name`.
+**/.git/config
+**/.git/modules/**/config
 
 # Agent scratch: one full checkout of the repo per in-flight agent.
 # Anchored because it occurs once where agents run at the repo root.
@@ -41,7 +51,9 @@
 **/[iI][dD]_[rR][sS][aA]
 **/[iI][dD]_[dD][sS][aA]
 **/[iI][dD]_[eE][cC][dD][sS][aA]
+**/[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
 **/[iI][dD]_[eE][dD]25519
+**/[iI][dD]_[eE][dD]25519_[sS][kK]
 
 # Dependencies: restored inside the image, never copied in.
 **/node_modules
@@ -62,5 +74,8 @@
 # This repo's own host-built binary (make build).
 /bin/mfer
 
-# The protoc script/bootstrap unpacks for script/generate.
+# The tools script/bootstrap installs for script/gofumpt and
+# script/generate.
+/bin/gofumpt
 /bin/protoc
+/bin/protoc-gen-go