[Enhancement] Complete frontend re-design and UI responsiveness Issues

### Context
Following the core architectural changes and LangGraph setup completed in PR #124, we need to focus on the frontend implementation.

### Problem
1. **Lack of Identity:** The current UI lacks a distinct brand identity and looks like a generic, AI-generated template. It does not reflect the project's design language.
2. **Disconnected Backend:** The frontend currently runs on hardcoded mock data and does not communicate with the FastAPI backend.
3. **Responsiveness:** The layout breaks on mobile devices (overlapping sidebars, hidden menus).

### Solution
- **UI Overhaul:** Replace the current generic interface with the custom design shared in the Discord channel (Figma).
- **Integration:** Connect the `PerspectivePage` to the real `/api/bias` and `/api/process` endpoints.
- **Mobile Support:** Implement a fully responsive layout with collapsible sidebars and hamburger menus.

### Tasks
- [x] Implement pixel-perfect Landing Page from Figma.
- [x] Build `BiasGauge` and `RightSidebar` components matching the new design.
- [x] Create `usePerspective` hook for real-time API data fetching.
- [x] Fix NLTK threading crashes in the backend to support the new frontend requests.