build(docs): migrate from pnpm to npm

Author: snowdream

docs/guide/quickstart.md

@@ -46,7 +46,7 @@ Open your project in any supported AI IDE and run the init workflow:
 This triggers the AI agent to:
 
 - Enable zero-config Node.js environment via `corepack enable`
-- Install all project-local linters and formatters via `pnpm install`
+- Install all project-local linters and formatters via `npm install`
 - Configure platform-specific tools (Homebrew / APT / Scoop)
 - Activate pre-commit hooks