Add OBS widgets for streamers

- Add widget token authentication system
- Create leaderboard, current assignment, and progress widgets
- Support dark, light, and neon themes
- Add widget settings modal for URL generation
- Fix avatar loading through backend API proxy

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/models/widget_token.py

@@ -0,0 +1,22 @@
+from datetime import datetime
+from sqlalchemy import DateTime, ForeignKey, String, Boolean
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+
+class WidgetToken(Base):
+    """Токен для авторизации OBS виджетов"""
+    __tablename__ = "widget_tokens"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    token: Mapped[str] = mapped_column(String(64), unique=True, index=True)
+    participant_id: Mapped[int] = mapped_column(ForeignKey("participants.id", ondelete="CASCADE"))
+    marathon_id: Mapped[int] = mapped_column(ForeignKey("marathons.id", ondelete="CASCADE"))
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+    expires_at: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True)
+
+    # Relationships
+    participant: Mapped["Participant"] = relationship("Participant")
+    marathon: Mapped["Marathon"] = relationship("Marathon")