docs: stop the Ask AI stream when the panel is closed

Closing only hid the panel; useChat stayed mounted and the in-flight stream +
searchDocs work kept consuming quota. Call stop() on close.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ouiliame

apps/docs/components/ai/ask-ai.tsx

@@ -102,7 +102,10 @@ export function AskAI({ locale }: AskAIProps) {
             <button
               type='button'
               aria-label='Close'
-              onClick={() => setOpen(false)}
+              onClick={() => {
+                stop()
+                setOpen(false)
+              }}
               className='flex size-7 items-center justify-center rounded-md text-[var(--text-icon)] transition-colors hover:bg-[var(--surface-active)]'
             >
               <X className='size-[16px]' />