cibuild: the org model, which runs every check uncached (closes #37)

script/cibuild was a plain docker build ., so on a tree Docker had
seen before every check step came from the build cache and the build
still passed. It is now the org model from sneak/prompts, byte for
byte: it runs script/bootstrap and script/check, then builds the image
with --no-cache and the git describe version as the VERSION build
argument, which the Dockerfile's builder stage already declares.
README.md's entry for the script says what it now does.

Model: opus-5-5

script/cibuild

@@ -1,15 +1,29 @@
 #!/bin/sh
-# script/cibuild: run the CI build: build the one image from Dockerfile,
-# whose stages run the checks as build steps (the backend's fmt-check,
-# lint and tests, and the frontend's test, lint and fmt-check). This is
-# the only build step the Gitea workflow runs.
+# script/cibuild: run the CI build. It bootstraps first: a CI runner
+# checks out and runs this and nothing else, and script/fmt-check runs
+# the formatter on the host, which a pristine checkout cannot do.
+# --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
 
-ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    timeout 300 docker build .
+    "$SCRIPT_DIR/bootstrap"
+    "$SCRIPT_DIR/check"
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`, so the inline form degrades silently to an
+    # empty constant. VERSION is computed here because .dockerignore
+    # excludes .git, so `git describe` in a build stage yields an empty
+    # version without failing.
+    version="$(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 "$@"