Port Docs-Viewer to slatehtml as the docs-viewer package.

Replace the classic DOM shell with slate widgets, markdown→slate rendering, and a CI index build that uses build-docs.cjs.

src/prose.css

@@ -0,0 +1,89 @@
+/* Article / highlight extras for docs-viewer (import alongside the viewer). */
+
+.md-collapse {
+  margin: 0;
+}
+
+/* Depth rhythm for nested heading collapses (OG markdown-content h2/h3). */
+.md-collapse[data-heading="3"] .slate-collapse-header {
+  margin: 2rem 0 0.75rem;
+}
+
+.md-collapse[data-heading="3"] .slate-collapse-title-text {
+  font-size: 1.5rem;
+  font-weight: 600;
+}
+
+.md-collapse[data-heading="4"] .slate-collapse-header,
+.md-collapse[data-heading="5"] .slate-collapse-header,
+.md-collapse[data-heading="6"] .slate-collapse-header {
+  margin: 1.5rem 0 0.5rem;
+}
+
+.md-collapse[data-heading="4"] .slate-collapse-title-text,
+.md-collapse[data-heading="5"] .slate-collapse-title-text,
+.md-collapse[data-heading="6"] .slate-collapse-title-text {
+  font-size: 1.15rem;
+  font-weight: 600;
+}
+
+.md-heading-flash {
+  animation: docs-heading-flash 1.1s ease;
+}
+
+@keyframes docs-heading-flash {
+  0% {
+    background: color-mix(in srgb, var(--accent, #2196f3) 35%, transparent);
+  }
+  100% {
+    background: transparent;
+  }
+}
+
+/* highlight.js-ish tokens (minimal, theme via currentColor) */
+.hljs {
+  color: inherit;
+  background: transparent;
+}
+.hljs-comment,
+.hljs-quote {
+  opacity: 0.55;
+  font-style: italic;
+}
+.hljs-keyword,
+.hljs-selector-tag,
+.hljs-built_in,
+.hljs-name,
+.hljs-tag {
+  color: var(--docs-syntax-keyword, #c6a0f6);
+}
+.hljs-string,
+.hljs-title,
+.hljs-section,
+.hljs-attribute,
+.hljs-literal,
+.hljs-template-tag,
+.hljs-template-variable,
+.hljs-type,
+.hljs-addition {
+  color: var(--docs-syntax-string, #a6da95);
+}
+.hljs-deletion,
+.hljs-selector-attr,
+.hljs-selector-pseudo,
+.hljs-meta {
+  color: var(--docs-syntax-meta, #ed8796);
+}
+.hljs-doctag,
+.hljs-number,
+.hljs-regexp {
+  color: var(--docs-syntax-number, #f5a97f);
+}
+.hljs-symbol,
+.hljs-variable,
+.hljs-template-variable,
+.hljs-link,
+.hljs-selector-id,
+.hljs-selector-class {
+  color: var(--docs-syntax-symbol, #8aadf4);
+}