feat(docs): Add scroll-to-top button for documentation pages

src/components/ScrollToTopButton/index.js

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+import React, { useState, useEffect } from "react";
+import styles from "./styles.module.css";
+
+export default function ScrollToTopButton() {
+  const [visible, setVisible] = useState(false);
+
+  useEffect(() => {
+    const onScroll = () => setVisible(window.scrollY > 300);
+    window.addEventListener("scroll", onScroll, { passive: true });
+    return () => window.removeEventListener("scroll", onScroll);
+  }, []);
+
+  const scrollToTop = () => {
+    window.scrollTo({ top: 0, behavior: "smooth" });
+  };
+
+  if (!visible) return null;
+
+  return (
+    <button
+      className={styles.scrollToTop}
+      onClick={scrollToTop}
+      aria-label="Scroll to top"
+      title="Scroll to top"
+    >
+      ↑
+    </button>
+  );
+}

src/components/ScrollToTopButton/styles.module.css

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+.scrollToTop {
+  position: fixed;
+  bottom: 2rem;
+  right: 2rem;
+  z-index: 999;
+  width: 2.5rem;
+  height: 2.5rem;
+  border-radius: 50%;
+  border: none;
+  background-color: var(--ifm-color-primary);
+  color: #fff;
+  font-size: 1.2rem;
+  line-height: 1;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.25);
+  transition: background-color 0.2s, opacity 0.2s, transform 0.2s;
+  opacity: 0.85;
+}
+
+.scrollToTop:hover {
+  opacity: 1;
+  transform: translateY(-2px);
+}

src/theme/Root.js

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+import React from "react";
+import ScrollToTopButton from "@site/src/components/ScrollToTopButton";
+
+export default function Root({ children }) {
+  return (
+    <>
+      {children}
+      <ScrollToTopButton />
+    </>
+  );
+}