chore: re-vendor canonical files from prompts at dd4027b (closes #472)

Copies .dockerignore, .gitignore, .prettierignore, check.yml and
REPO_POLICIES.md from sneak/prompts at dd4027b. The repo's own entries
(dist/, release/, yarn files) are kept after the canonical content.

The Dockerfile gets separate lint and test phases. Its last stage
depends on both, checks the git describe version and runs make build.
script/lint, test, check, cibuild and docker are the canonical models.
check-censored moves into the lint phase and test-verify-build into the
test phase. fmt and fmt-check fall back to the nvm-installed node. The
e2e image builds are uncached. Comments that cited the old test caps
now say 60 seconds, and comments that named what runs a script now name
the Dockerfile phase or stage.

Model: opus-5-5

script/lib/eslint/noStateSingletonInBackground.js

@@ -14,7 +14,7 @@
 // the build when esbuild's own metafile reports src/shared/state.js as an input
 // of a background bundle. That consults the resolution esbuild actually
 // performed, so no specifier syntax and no resolution rule can slip past it,
-// and Dockerfile:42 runs `make build` in CI.
+// and the Dockerfile's last stage runs `make build` in CI.
 //
 // What this rule is: fast local feedback, in the editor and in `make lint`,
 // before a full bundle. It reads sources from disk and matches import