Refactor: Remove Stage 2 Peer Ranking & Overhaul UI for Concurrent Chats

[Karanpratap7]

Summary

This PR streamlines the LLM Council process by removing the experimental "Peer Ranking" (Stage 2) phase to improve performance and response latency. It also introduces a major UI overhaul, featuring a modern dark theme and support for concurrent chat sessions.

Key Changes

1. Unified & Improved Workflow

• Removed Stage 2: The backend now proceeds directly from Stage 1 (Individual Responses) to Stage 3 (Chairman Synthesis), reducing overhead.
• Backend Cleanup: Removed unused Stage 2 logic and event emitters from [council.py]

2. Frontend Architecture

• Concurrent Chats: Refactored App.jsx to use a conversationsMap state. You can now switch between chats without interrupting background generation in other active sessions.
• Real-time Updates: State management now correctly handles streaming updates for non-active conversations.

3. UI/UX Modernization

• New Aesthetic: Implemented a premium dark theme (#1e1e1e backgrounds, Inter font, bubble-style messages).
• Sidebar: Redesigned with clear active states and a new "New Chat" button.
• Messaging: Added per-message loading indicators (e.g., "Collecting responses...", "Synthesizing...") replacing the global full-screen loader.

Verification

• Verified that the pipeline runs successfully from Stage 1 to Stage 3.
• Confirmed that switching tabs during generation preserves the streaming state.
• Checked that the new UI styles are applied correctly across the app.