[CCUBE-2223][XY] Add Flagship DS agent skills

[ninjasheeps]

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing apis or functionality to change)
• Documentation (change to documentation, comments or API descriptions)
• Tests (improvements to unit tests or E2E tests)
• Other (technical improvements, refactoring, or changes that don't fall into the above categories)

Description of changes

• Link to ticket
• Add fds-build agent skill which allows consumers to build web pages/applications using FDS
• Covers component selection, import paths, theming setup, layout patterns, and common mistakes for both v3 and v4
• Props tables auto-generated from TypeScript source via scripts/generate-skill-props.ts
• 11 evals included for validation
• Install via npx skills add lifesg/react-design-system
• Currently the skill supports building form/listing pages, will be adding more templates in the future

Checklist

• Changes follow the project guidelines in CONTRIBUTING.md and CONVENTIONS.md
• Looks good on mobile and tablet
• Updated documentation
• Added/updated unit tests
• Added/updated E2E tests