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/alembic/versions/029_add_widget_tokens.py

@@ -0,0 +1,36 @@
+"""Add widget tokens
+
+Revision ID: 029
+Revises: 028
+Create Date: 2025-01-09
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = '029_add_widget_tokens'
+down_revision = '028_add_promo_codes'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        'widget_tokens',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('token', sa.String(64), nullable=False),
+        sa.Column('participant_id', sa.Integer(), nullable=False),
+        sa.Column('marathon_id', sa.Integer(), nullable=False),
+        sa.Column('created_at', sa.DateTime(), nullable=False),
+        sa.Column('expires_at', sa.DateTime(), nullable=True),
+        sa.Column('is_active', sa.Boolean(), nullable=False, server_default='true'),
+        sa.PrimaryKeyConstraint('id'),
+        sa.ForeignKeyConstraint(['participant_id'], ['participants.id'], ondelete='CASCADE'),
+        sa.ForeignKeyConstraint(['marathon_id'], ['marathons.id'], ondelete='CASCADE'),
+    )
+    op.create_index('ix_widget_tokens_token', 'widget_tokens', ['token'], unique=True)
+
+
+def downgrade():
+    op.drop_index('ix_widget_tokens_token', table_name='widget_tokens')
+    op.drop_table('widget_tokens')