Pin tailwindcss and check the committed stylesheet against it (closes #231)

make css ran whatever tailwindcss binary was on the host's PATH, so the committed stylesheet depended on the machine that built it, and nothing noticed when a template used a class the stylesheet lacked. make css now runs the standalone tailwindcss v4.2.1, pinned by sha256, in a Dockerfile stage, and a check stage, run by make check and required by the image build, fails when the committed static/css/tailwind.css differs from what the templates need, showing the differing rules. input.css names its sources. The unused .btn-text is removed and the stylesheet regenerated, dropping only unused rules. The README has a Stylesheet section.

Model: opus-5-5

script/bootstrap

@@ -60,9 +60,9 @@ main() {
     if missing go; then pkg_install go golang go go; fi
 
     # Not installed here: docker is platform-specific and out of scope for a
-    # package-manager bootstrap, but script/lint needs it.
+    # package-manager bootstrap, but script/lint and script/css need it.
     if missing docker; then
-        echo "bootstrap: docker not found; script/lint requires it" >&2
+        echo "bootstrap: docker not found; script/lint and script/css require it" >&2
     fi
 
     go mod download

script/check

@@ -1,8 +1,8 @@
 #!/bin/sh
-# script/check: run all checks (test, lint, fmt-check). Our own
+# script/check: run all checks (test, lint, fmt-check, css-check). Our own
 # extension to scripts-to-rule-them-all.
 # Writes only the ignored static/js/alpine.min.js, through script/test.
-# Generic: usually needs no adaptation.
+# Generic, apart from css-check.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
@@ -11,6 +11,7 @@ main() {
     "$SCRIPT_DIR/test"
     "$SCRIPT_DIR/lint"
     "$SCRIPT_DIR/fmt-check"
+    "$SCRIPT_DIR/css-check"
 }
 
 main "$@"

script/css

@@ -0,0 +1,15 @@
+#!/bin/sh
+# script/css: regenerate static/css/tailwind.css (writes). tailwindcss is
+# never installed locally: it runs in docker, at the version and sha256
+# pinned in the Dockerfile's stylesheet stages, which also say what the
+# stylesheet is generated from.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    docker build --target css-output --output type=local,dest=static/css .
+}
+
+main "$@"

script/css-check

@@ -0,0 +1,14 @@
+#!/bin/sh
+# script/css-check: fail when static/css/tailwind.css differs from what
+# script/css would generate (read-only). The comparison is the Dockerfile's
+# css-check stage, which the image build runs too.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    docker build --target css-check --output type=cacheonly .
+}
+
+main "$@"