Phase-3: Implement Interactive Next.js UI + Token Streaming + Attention Visualization

[Vishal-sys-code]

Summary:

This PR delivers Phase 3 of the Cognify.AI project - the first fully functional Interactive Frontend MVP, built with Next.js, React, and TailwindCSS, integrating tightly with the backend WebSocket streaming API.

This release introduces:

• A full Playground UI for prompt submission, LLM selection, and Chain-of-Thought toggling
• Real-time token streaming over WebSocket
• Token Timeline visualization with activation bars
• Attention Heatmap viewer (thumbnail + full-resolution rendering)
• CoT (Chain-of-Thought) Panel and token linking
• Session Viewer for loaded/in-progress sessions
• Session Sharing (shareable permalink)
• Robust handling of WS reconnection, streaming fallback, and artifact fetching

This is the first version of the Cognify.AI frontend that can be shown publicly and serves as the foundation for future research visualizations.

Implemented by: @Vishal-sys-code