perf: optimize docs static generation cost (#12108)

## Summary
- Switch the docs catch-all route to full static generation and prebuild
both latest and versioned docs paths.
- Prebuild OG images for all docs pages, make sitemap and LLM export
static, and remove nondeterministic sitemap timestamps.
- Reduce build-time overhead by memoizing docs sidebar trees and
skipping processed markdown generation for versioned docs.

## Testing
- `pnpm nx run @zitadel/docs:build`
- `pnpm nx run @zitadel/docs:lint`
- `pnpm nx run @zitadel/docs:check-types`
- Verified the prerender manifest contains 8,816 prerendered routes,
3,293 versioned docs routes, 4,406 OG routes, and zero revalidating docs
routes.

apps/docs/app/sitemap.ts

@@ -1,27 +1,26 @@
 import { MetadataRoute } from 'next';
 import { source } from '@/lib/source';
 
+export const revalidate = false;
+export const dynamic = 'force-static';
+
 export default function sitemap(): MetadataRoute.Sitemap {
-    const baseUrl = 'https://zitadel.com/docs';
+  const baseUrl = 'https://zitadel.com/docs';
 
-    const docsPages = source.getPages().map((page) => ({
-        url: `${baseUrl}${page.url === '/' ? '' : page.url}`,
-        lastModified: new Date(),
-        changeFrequency: 'weekly' as const,
-        priority: 0.8,
-    }));
+  const docsPages = source.getPages().map((page) => ({
+    url: `${baseUrl}${page.url === '/' ? '' : page.url}`,
+    changeFrequency: 'weekly' as const,
+    priority: 0.8,
+  }));
 
-
-
-    return [
-        {
-            url: baseUrl,
-            lastModified: new Date(),
-            changeFrequency: 'daily' as const,
-            priority: 1,
-        },
-        ...docsPages,
-    ].filter((item, index, self) =>
-        index === self.findIndex((t) => t.url === item.url)
-    );
+  return [
+    {
+      url: baseUrl,
+      changeFrequency: 'daily' as const,
+      priority: 1,
+    },
+    ...docsPages,
+  ].filter(
+    (item, index, self) => index === self.findIndex((t) => t.url === item.url),
+  );
 }