Bump Next.js from 15.4.5 to 15.5.6 and update related dependencies.
Also upgrade other packages to latest compatible versions including: -
Radix UI components (all minor version updates) - Tiptap editor (3.0.7 →
3.11.0) - React and React DOM (19.1.1 → 19.2.0) - TanStack Query (5.84.0
→ 5.90.10) - TypeScript and ESLint ecosystem - Tailwind CSS (4.1.11 →
4.1.17) - Various other patch and minor updates
Additionally add theme support with next-themes and multiple color
schemes (light, dark, sunset, forest).
