Re-vendor the shared files from sneak/prompts at dd4027b (closes #504)

Fetches the shared files unchanged from sneak/prompts commit dd4027b and
adds .prettierignore; .dockerignore keeps this repository's anchored host
artifacts at its end.

Linting moves into the Dockerfile's lint phase on the golangci-lint
v2.14.0 image, which also runs the js-lint stage, and Dockerfile.lint is
gone. Tests move into a test phase on the golang bookworm image.
script/lint, test, docker and cibuild are the model scripts, every docker
build in script/ passes --no-cache, and the .ci-fingerprint barrier is
gone. The workflow no longer calls script/ci-mark-superseded, so it and
its tests are removed. make build passes -trimpath and -s -w.

Model: opus-5-5

.gitea/workflows/check.yml

@@ -1,37 +1,9 @@
 name: check
-
-on:
-  push:
-    branches:
-      - '**'
-
+on: [push]
 jobs:
-  check:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2 2024-10-23
-        with:
-          # The superseded-status step needs history to walk ancestors (it
-          # aborts on a shallow clone).
-          fetch-depth: 0
-
-      - name: Mark superseded run statuses
-        # Gitea cancels the in-flight run when another commit is pushed to the
-        # same branch and records the cancellation as `failure`, so a commit
-        # that was never tested reads as a test result. The script rewrites
-        # those statuses to say what happened. See its header for why the
-        # state stays `failure` and not `skipped`.
-        env:
-          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
-        run: script/ci-mark-superseded
-
-      - name: Fingerprint the build context
-        # Writes the hash of the commit being checked into the context, which
-        # invalidates the `COPY . .` layer of every check stage: a commit
-        # that was never linted, format-checked, stylesheet-checked, tested
-        # and built cannot report success from cache.
-        run: git rev-parse HEAD > .ci-fingerprint
-
-      - name: Build Docker image (runs the gofmt check, golangci-lint, the stylesheet check, ESLint, the Markdown check, make test, make build)
-        run: script/cibuild
+    check:
+        runs-on: ubuntu-latest
+        steps:
+            # actions/checkout v4.2.2, 2026-02-22
+            - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+            - run: script/cibuild