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 20-second
test cap now say 60.

Model: opus-5-5

docs/RELEASE.md

@@ -16,9 +16,9 @@ so the "release commit" throughout is the `main` commit the milestone PR merged.
 ## Procedure
 
 1. **Confirm `main` is green in CI.** The `check` workflow
-   (`.gitea/workflows/check.yml`) runs `script/cibuild`, i.e. `docker build .`,
-   and the `Dockerfile` runs `make check` as a build step, so a green `check`
-   run is a green `make check`. Find the run for the exact release commit on the
+   (`.gitea/workflows/check.yml`) runs `script/cibuild`, which runs
+   `script/check` and then builds the image uncached, so a green `check` run is
+   a green `make check`. Find the run for the exact release commit on the
    tracker's Actions view. _Check:_ that commit's `check` run succeeded; running
    `make check` on a clean checkout of the commit reproduces it and exits 0.