improvement(docs): remove Ask AI, add the missing platform surfaces, align the sidebar (#6259)

* improvement(docs): remove Ask AI, add missing surfaces, align sidebar to the app

- Removes the Ask AI widget, its /api/chat route, and the four deps exclusive
  to it (@ai-sdk/openai, @ai-sdk/react, ai, streamdown). lib/embeddings and
  docsEmbeddings stay — /api/search uses them.
- Adds --surface-7 and --surface-hover, the last two platform surfaces docs
  lacked.
- Aligns the sidebar with the app's canonical nav chrome: px-2.5 -> px-2,
  text-small -> text-sm, hover --surface-3 -> --surface-active, and an active
  hover of --surface-6, matching the Chip the app's sidebar items are built on.

* fix(docs): make the sidebar hover CSS agree with the utilities

Review caught that the sidebar hover alignment in this PR had no visual
effect. `global.css` carries !important rules for both the link and button
sidebar items — they exist to beat fumadocs' own styles — and they were still
forcing the pre-alignment values: --surface-3 on an inactive hover, and
--surface-active on an active hover.

So the Tailwind utilities were dead on arrival. The global rules now carry the
app's values instead (--surface-active inactive, --surface-6 active), matching
the utilities rather than fighting them, with a comment noting the two must
move together.

Author: waleedlatif1

apps/docs/app/[lang]/layout.tsx

@@ -3,7 +3,6 @@ import { defineI18nUI } from 'fumadocs-ui/i18n'
 import { DocsLayout } from 'fumadocs-ui/layouts/docs'
 import { RootProvider } from 'fumadocs-ui/provider/next'
 import { Geist_Mono, Inter } from 'next/font/google'
-import { AskAI } from '@/components/ai/ask-ai'
 import {
   SidebarFolder,
   SidebarItem,
@@ -124,7 +123,6 @@ export default async function Layout({ children, params }: LayoutProps) {
             {children}
           </DocsLayout>
           <Footer />
-          <AskAI locale={lang} />
         </RootProvider>
       </body>
     </html>