feat: Initial project structure for WebTriviasMulti

- Backend: FastAPI + Python-SocketIO + SQLAlchemy
  - Models for categories, questions, game sessions, events
  - AI services for answer validation and question generation (Claude)
  - Room management with Redis
  - Game logic with stealing mechanics
  - Admin API for question management

- Frontend: React + Vite + TypeScript + Tailwind
  - 5 visual themes (DRRR, Retro, Minimal, RGB, Anime 90s)
  - Real-time game with Socket.IO
  - Achievement system
  - Replay functionality
  - Sound effects per theme

- Docker Compose for deployment
- Design documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/models/category.py

@@ -0,0 +1,18 @@
+from sqlalchemy import Column, Integer, String
+from sqlalchemy.orm import relationship
+from app.models.base import Base
+
+
+class Category(Base):
+    __tablename__ = "categories"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String(100), nullable=False, unique=True)
+    icon = Column(String(50))
+    color = Column(String(7))  # Hex color
+
+    # Relationships
+    questions = relationship("Question", back_populates="category")
+
+    def __repr__(self):
+        return f"<Category(id={self.id}, name='{self.name}')>"