Migrate built-in search to ZBSearch

Migrate built-in search to ZBSearch

Static Orama search now uses Fumadocs Core's staticClient backed by ZBSearch. The @orama/orama dependency was removed.

Use fumadocsMdx() Vite plugin

Scaffolded apps and docs examples now register the Fumadocs MDX Vite plugin via fumadocsMdx() instead of the default import.