add llm support

[warma16]

PR-Codex overview

This PR introduces a new plugin configuration for vitepress, enhancing the shared configuration with the addition of the llmstxt plugin.

Detailed summary

• Added import statement for llmstxt from vitepress-plugin-llms in .vitepress/sharedConfig.ts.
• Updated sharedConfig to include a vite object with a plugins array that initializes llmstxt().

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