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, keeping the repo's own
entries (dist/, release/, yarn files) 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 citing the old test caps or what
runs a script are updated.

Model: opus-5-5

tests/e2e/firefox/run.js

@@ -8,7 +8,7 @@
 //   node tests/e2e/firefox/run.js [dist/firefox]
 //
 // Deliberately not part of script/check, and deliberately not named
-// *.test.js: REPO_POLICIES.md caps make test at 20 seconds and a browser
+// *.test.js: REPO_POLICIES.md caps make test at 60 seconds and a browser
 // suite does not fit.
 //
 // This shares no driver layer with the Chrome suite in tests/e2e/, and the