docs: add comprehensive AI agent guide for workspace development

[miguelpinto98]

• Add AGENTS.md with complete workspace documentation
• Include monorepo structure and architecture overview
• Document StencilJS component concepts (Shadow DOM, themes, decorators)
• Provide component file structure patterns with examples
• Detail development workflow and essential commands
• Add comprehensive git commit message guidelines with real examples
• Include troubleshooting guide and quick reference card
• Document theme system and global configuration
• Explain React package entry points for CSR/SSR
• Add Storybook story categories and structure