Add comprehensive React + Next.js migration plan

Created detailed migration plan for rewriting Vuetify UI to modern React stack:
- Complete architecture design with Next.js 15 App Router
- React 18 + TypeScript 5 + Tailwind CSS v4
- All 25 Vue components mapped to React equivalents
- ServiceStack API integration strategy with React Query
- State management with Zustand + React Query
- 10-phase implementation plan (8-10 weeks)
- Modern UI design system with shadcn/ui + Radix
- SEO optimization and accessibility guidelines
- Performance targets and deployment strategy

The plan preserves the C# ServiceStack backend while providing complete
freedom to create a visually stunning modern React application.

Author: claude