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

make css now runs the standalone tailwindcss CLI, v4.2.1, pinned by
sha256, in a build stage of the Dockerfile instead of whatever
tailwindcss is on the host. A css-check stage, run by make check and
required by the image build, fails when static/css/tailwind.css differs
from what make css generates.

input.css now names its sources (the templates, app.js, and the Go file
that picks status colour classes) instead of letting the whole checkout
be scanned, where words in Go code and docs became unused classes.
.btn-text is removed and tailwind.css regenerated; it only loses unused
rules.

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 "$@"