docs: restructure versioned docs sidebar and add version-aware navbar

Unify sidebar structure across all doc versions to:
Overview, Quick start, Concepts, Examples/Guides, Upgrading, Changelog.

For v1.12, merge the multi-page Overview section into a single Overview
page and add a dedicated Quick start page. Rename directory from
overview to introduction for consistent doc IDs across versions.

Add custom VersionedReferenceNavbarItem component so the Reference tab
follows the selected docs version. Make Docs and Changelog tabs
version-aware using Docusaurus type: 'doc' navbar items.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vdusek

website/docusaurus.config.js

@@ -66,19 +66,21 @@ module.exports = {
                     title: 'API Client for Python',
                     items: [
                         {
-                            to: 'docs',
+                            type: 'doc',
+                            docId: 'introduction/introduction',
                             label: 'Docs',
                             position: 'left',
                             activeBaseRegex: '/docs(?!/changelog)',
                         },
                         {
-                            to: '/reference',
+                            type: 'custom-versioned-reference',
                             label: 'Reference',
                             position: 'left',
                             activeBaseRegex: '/reference',
                         },
                         {
-                            to: 'docs/changelog',
+                            type: 'doc',
+                            docId: 'changelog',
                             label: 'Changelog',
                             position: 'left',
                             activeBaseRegex: '/docs/changelog',

website/src/theme/NavbarItem/ComponentTypes.js

@@ -0,0 +1,7 @@
+import OriginalComponentTypes from '@theme-original/NavbarItem/ComponentTypes';
+import VersionedReferenceNavbarItem from './VersionedReferenceNavbarItem';
+
+export default {
+    ...OriginalComponentTypes,
+    'custom-versioned-reference': VersionedReferenceNavbarItem,
+};

website/src/theme/NavbarItem/VersionedReferenceNavbarItem.js

@@ -0,0 +1,16 @@
+import React from 'react';
+import { useDocsVersionCandidates } from '@docusaurus/plugin-content-docs/client';
+import DefaultNavbarItem from '@theme/NavbarItem/DefaultNavbarItem';
+
+/* eslint-disable react/prop-types */
+export default function VersionedReferenceNavbarItem({ docsPluginId, ...props }) {
+    const [version] = useDocsVersionCandidates(docsPluginId);
+
+    // Latest version → /reference, "current" (next) → /reference/next, others → /reference/{name}
+    let to = '/reference';
+    if (!version.isLast) {
+        to = `/reference/${version.name === 'current' ? 'next' : version.name}`;
+    }
+
+    return <DefaultNavbarItem {...props} to={to} />;
+}