[WIP] pnpm monorepo starter template, use antfu

[Copilot]

Setting up pnpm monorepo starter template with antfu's configuration:

• Explore repository structure (only README.md exists)
• Install pnpm globally
• Create pnpm workspace configuration
• Set up package.json with antfu's conventions
• Create monorepo structure with packages directory
• Add ESLint configuration (antfu's config)
• Add TypeScript configuration
• Add Prettier configuration
• Set up build tools (tsup/unbuild)
• Add testing setup (vitest)
• Create CI/CD workflows
• Add development scripts and tooling
• Update README with proper documentation
• Add example packages to demonstrate monorepo structure

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