fix(theme): restore article styles on doc pages

Overriding DocContent took the upstream module out of the bundle, and
with it the `doc.css` it imports as a side effect. Every page rendering
through DocLayout lost its article typography, table scroll container
and heading anchors — while the rest of the theme stayed intact, which
is why only some styles went missing.

The sole reference to the upstream component was a `typeof`, erased at
compile time, so the bundler saw a module it could drop.

- Delegate to the upstream component when a page has no hoisted bands,
  which keeps that module and its stylesheet in the dependency graph.
- Move the hoisting variant into its own component, so useScrollAfterNav
  is not called after a conditional return. DocContent survives
  client-side navigation, so its hook count has to stay constant.

theme/components/DocContent.tsx

@@ -1,6 +1,6 @@
 import type { ComponentProps } from "react"
 import { MDXProvider } from "@mdx-js/react"
-import { Content, usePage, useSite } from "@rspress/core/runtime"
+import { Content, useFrontmatter, usePage, useSite } from "@rspress/core/runtime"
 import {
   Callout,
   DocContent as OriginalDocContent,
@@ -27,23 +27,25 @@ function FallbackTitle() {
 }
 
 /**
- * Mirrors `@rspress/core`'s `DocContent`, with one addition: the bands a page
+ * Upstream's `DocContent`, with one addition: the bands a page marks
- * marks `placement: top` render between the page title and the article body.
+ * `placement: top` render between the page title and the article body.
  *
  * Rspress has no slot for that position. `beforeDocContent` sits above the
  * title, and `afterDocContent` and the `Layout`'s `afterDoc` both sit below the
  * whole article — which is why sections used to land at the foot of the
- * products page. Replacing this component is the only way in, so it is a
+ * products page. Replacing the component is the only way in.
- * deliberate copy of upstream and is worth re-diffing whenever Rspress is
- * upgraded. Everything below comes straight from upstream: `useScrollAfterNav`
- * restores the scroll position after a client-side navigation, and the MDX
- * component map is layered as defaults, then the caller's overrides, then the
- * placeholder the compiled MDX uses for callouts.
  *
- * Every page rendering through `DocLayout` goes through here, so be careful:
+ * Everything except the inserted `<HomeSections>` is copied from upstream:
- * a mistake affects blogs and project pages as much as the marketing ones.
+ * `useScrollAfterNav` restores the scroll position after a client-side
+ * navigation, and the MDX component map is layered as defaults, then the
+ * caller's overrides, then the placeholder the compiled MDX uses for callouts.
+ * Worth re-diffing whenever Rspress is upgraded.
+ *
+ * A separate component rather than a branch inside `DocContent`, because the
+ * hook below must not be called conditionally — `DocContent` survives
+ * client-side navigation, so the number of hooks it calls has to stay constant.
  */
-export function DocContent({
+function HoistedDocContent({
   components,
   isOverviewPage = false,
   beforeDocContent,
@@ -67,3 +69,25 @@ export function DocContent({
     </MDXProvider>
   )
 }
+
+/**
+ * Renders the page body. Pages with nothing to hoist delegate to upstream
+ * rather than re-rendering its markup here.
+ *
+ * That is not only about drift. Upstream's module carries `doc.css` as a
+ * side-effect import, and the only reference to the component above is in a
+ * `typeof` — which a bundler may treat as no reference at all. It then drops
+ * the module, and the article stylesheet is dropped with it. Keeping a real
+ * render path to upstream is what holds those styles in the bundle.
+ */
+export function DocContent(props: DocContentProps) {
+  const { frontmatter } = useFrontmatter()
+
+  const raw = frontmatter?.sections
+  const hasHoistedBands =
+    Array.isArray(raw) &&
+    raw.some((entry) => (entry as { placement?: unknown } | null)?.placement === "top")
+
+  if (!hasHoistedBands) return <OriginalDocContent {...props} />
+  return <HoistedDocContent {...props} />
+}