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/source.config.ts

@@ -39,9 +39,6 @@ export const versions = defineDocs({
       sidebar_label: z.string().optional(),
     }),
     files: ['v*/**/*.md', 'v*/**/*.mdx', '!**/_*'], // Include only versioned folders from content
-    postprocess: {
-      includeProcessedMarkdown: true,
-    },
   },
   meta: {
     schema: metaSchema,