feat: add Alembic database migrations

Replace create_all() startup approach with Alembic for proper schema
versioning. Includes initial migration for users and evotor_connections
tables, entrypoint script that runs migrations before starting uvicorn.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -13,6 +13,8 @@ services:
       - BASE_URL=${BASE_URL:-http://localhost:8080}
     volumes:
       - ./web:/app/web
+      - ./alembic.ini:/app/alembic.ini
+      - ./docker-entrypoint.sh:/app/docker-entrypoint.sh
 
   sync:
     build: