Make lint and test phases of the Dockerfile (closes #96)

Follows the template: Dockerfile.lint is gone; the Dockerfile has a lint
phase (eslint, prettier --check .) and a test phase (vitest, run as the
node user, which the not-writable-directory tests need), and its
last stage compiles and depends on both. script/lint and script/test
build one phase each with --no-cache; script/docker and script/cibuild
pass --no-cache, so CHECK_EPOCH and LINT_EPOCH are removed.
script/cibuild is the single image build, so CI runs lint and the tests
once each. The tests that checked the old layout are deleted,
REPO_POLICIES.md is re-copied and the README describes the new layout.

Model: opus-5-5

script/cibuild

@@ -1,15 +1,11 @@
 #!/bin/sh
-# script/cibuild: run the CI build, which is both images in a defined order.
-#
-# First script/lint, which builds Dockerfile.lint and is the one and only
-# place linting happens — it goes first so a lint failure is reported before
-# the slower suite runs. Then the Dockerfile image, which runs script/test
-# and script/build. CHECK_EPOCH and LINT_EPOCH differ on every invocation, so
-# neither the linters nor the suite can be served from Docker's cache: a
-# green build here means the checks ran now, not that a previous run was
-# remembered. The layers below the epochs (bootstrap, yarn install) are
-# unaffected and stay cached. A build that omits the arguments fails by
-# design.
+# script/cibuild: run the CI build. The image's last stage depends on the
+# lint and test phases, so this one build runs eslint, prettier and the
+# suite once each and then compiles. Unlike the template it does not run
+# script/check first, which would run lint and the tests a second time.
+# --no-cache for the same reason as script/docker: the gate phases the
+# final stage depends on are RUN steps, and a cached one is a check that
+# did not run.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -17,8 +13,16 @@ ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    "$SCRIPT_DIR/lint"
-    docker build --build-arg CHECK_EPOCH="$(date +%s)" .
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. VERSION is computed here because .dockerignore
+    # excludes .git, so `git describe` in a build stage yields an empty
+    # version without failing.
+    version="$(git describe --tags --always --dirty 2>/dev/null || true)"
+    [ -n "$version" ] || version="unknown"
+    docker build --no-cache \
+        --build-arg VERSION="$version" \
+        -t "$("$SCRIPT_DIR/projectname")" .
 }
 
 main "$@"