fix(vuepress): add @vite-ignore to LazyMermaid dynamic import

Rolldown (Vite 8) tries to statically analyze and bundle dynamic imports
at build time, failing with UNLOADABLE_DEPENDENCY because it cannot load
the plugin's client component via the package exports glob pattern.

Adding /* @vite-ignore */ skips build-time bundling and leaves the import
to resolve correctly at runtime, matching local dev behavior.

Co-authored-by: Cursor <cursoragent@cursor.com>