feat(docs): add documentation site and demo features

- Introduced a new documentation site for Cursor BYOK using Next.js and Fumadocs.
- Added a product demo page with a corresponding Vite configuration.
- Implemented a demo API to simulate LLM calls and responses.
- Enhanced the Makefile to include new build and development commands for the documentation.
- Updated package.json scripts for building and running the documentation site.
- Created various components and layouts for the documentation structure, including blog and user documentation sections.
- Added styling for the new components and layouts to ensure a cohesive design.
- Included a README and other necessary files for local development and deployment.

apps/desktop/package.json

@@ -10,6 +10,7 @@
     "typecheck:node": "tsc --noEmit -p tsconfig.node.json",
     "i18n:scan": "STATIC_I18N_SCAN=true vite build",
     "build": "vite build",
+    "build:demo": "npm run typecheck && npm run typecheck:node && vite build --config vite.demo.config.ts",
     "check": "npm run typecheck && npm run typecheck:node && npm run build",
     "dev:web": "concurrently --kill-others --success first --names server,web \"cross-env CURSOR_CONSOLE_PROXY=http://127.0.0.1:1420 cargo run --manifest-path ../../server/Cargo.toml --bin cursor-server\" \"wait-on http-get://127.0.0.1:3000/__byok-api__/healthz && vite\"",
     "serve": "vite preview",