Install SQLAlchemy's asyncio extra so greenlet ships in the image

A clean `pip install .` in the Docker image left out greenlet, so
`alembic upgrade head` crashed on import of sqlalchemy.ext.asyncio and
the container restart-looped.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pyproject.toml

@@ -5,7 +5,7 @@ requires-python = ">=3.12"
 dependencies = [
     "fastapi>=0.115",
     "uvicorn[standard]>=0.32",
-    "sqlalchemy>=2.0",
+    "sqlalchemy[asyncio]>=2.0",
     "aiosqlite>=0.20",
     "alembic>=1.13",
     "pydantic-settings>=2.6",