- Replace Bauhaus aesthetic with Material Design 3-inspired layout
- Add working grade/subject/chapter dropdown selectors with placeholder options
- Fix ChatInput layout: remove position:absolute, use flex column flow
- Update sidebar with Material Icons, upgrade card, and clean hover states
- Add TopNav dropdowns with click-outside-to-close behavior
- Modernize message bubbles, action buttons, and welcome state
- Replace SVG icons with Material Symbols throughout
- Apply consistent BEM naming, CSS custom properties, no inline styles
- Add TopNav component with AI Chat, Study Guides, Progress tabs
- Refactor sidebar to include brand, new chat, subjects, chat history, settings
- Add message action buttons (Helpful, Note, Deeper) on assistant responses
- Enhance ChatInput with photo, mic attachment icons and AI disclaimer
- Improve welcome state with 2x2 suggested prompt grid
- Update global layout for proper sidebar offset (fix nav overlap)
- Remove obsolete Header component
- All styles: strict BEM naming, zero inline CSS, Paper Look theme
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