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

script/test-e2e-firefox

@@ -4,7 +4,7 @@
 # script/test-e2e. Our own extension to scripts-to-rule-them-all.
 #
 # Deliberately NOT called by script/check or script/test, for the same
-# reason as the Chrome suite: REPO_POLICIES.md caps make test at 20 seconds
+# reason as the Chrome suite: REPO_POLICIES.md caps make test at 60 seconds
 # and a browser suite does not fit. .gitea/workflows/e2e.yml also runs it
 # on every push, in a job separate from check.
 #
@@ -44,7 +44,9 @@ main() {
     trap 'cleanup; exit 130' INT TERM
 
     echo "Building the pinned Firefox e2e image (extension included)..."
-    docker build --iidfile "$IIDFILE" -t "$IMAGE" \
+    # --no-cache: the image build runs make build and its checks, and a
+    # cached layer is a check that did not run.
+    docker build --no-cache --iidfile "$IIDFILE" -t "$IMAGE" \
         -f tests/e2e/firefox/Dockerfile .
 
     echo "Running the Firefox e2e suite..."