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/__init__.py

@@ -18,6 +18,7 @@ from app.models.inventory import UserInventory
 from app.models.coin_transaction import CoinTransaction, CoinTransactionType
 from app.models.consumable_usage import ConsumableUsage
 from app.models.promo_code import PromoCode, PromoCodeRedemption
+from app.models.widget_token import WidgetToken
 
 __all__ = [
     "User",
@@ -65,4 +66,5 @@ __all__ = [
     "ConsumableUsage",
     "PromoCode",
     "PromoCodeRedemption",
+    "WidgetToken",
 ]