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-entrypoint.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+set -e
+alembic upgrade head
+exec uvicorn web.main:app --host 0.0.0.0 --port 8000