docs: add one-command README HTML/PDF export

docs/docinfo.html

@@ -0,0 +1,58 @@
+<!-- Injected by Asciidoctor when generating the print/PDF HTML variant.
+     Usage: asciidoctor -a docinfodir=docs -a docinfo=shared README.adoc -o README-print.html
+     Fixes color-emoji rendering in headless Chromium and adapts the layout for print. -->
+<style>
+/* Font stacks with an explicit emoji fallback. "Noto Color Emoji" must be
+   installed system-wide (package: fonts-noto-color-emoji). */
+* {
+    font-family: "Noto Sans", "Noto Color Emoji", sans-serif !important;
+}
+pre, code, kbd, samp {
+    font-family: "Noto Sans Mono", "Noto Color Emoji", monospace !important;
+}
+
+@media print {
+    /* The left-floating TOC is screen-only; bring it back into the flow */
+    #header, #toc {
+        position: static !important;
+        width: auto !important;
+        max-width: none !important;
+        float: none !important;
+        height: auto !important;
+        overflow: visible !important;
+    }
+    #content {
+        margin: 0 !important;
+        padding: 0 !important;
+        max-width: none !important;
+    }
+    body {
+        margin: 0;
+        font-size: 10pt;
+        line-height: 1.35;
+    }
+    /* Keep headings with their content, break tables between rows only */
+    h1, h2, h3, h4, h5, h6 {
+        page-break-after: avoid;
+    }
+    tr, td, th, .admonitionblock, .imageblock {
+        page-break-inside: avoid;
+    }
+    /* Long code listings may overflow the page width: allow wrapping */
+    pre {
+        white-space: pre-wrap;
+        word-wrap: break-word;
+    }
+    img {
+        max-width: 100%;
+    }
+    /* Links are not clickable in a PDF: keep them readable, not blue */
+    a {
+        color: inherit;
+        text-decoration: none;
+    }
+    a[href^="http"]::after {
+        content: "";
+    }
+}
+</style>