feat: SQLAlchemy async database setup

fablednetmon/database.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+from typing import TYPE_CHECKING
+from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
+
+if TYPE_CHECKING:
+    from quart import Quart
+
+
+def init_db(app: "Quart") -> None:
+    """Create async engine and attach db_sessionmaker to app.
+
+    Called during create_app() after config is loaded.
+    Does not create tables — Alembic handles migrations.
+    """
+    db_url: str = app.config["DATABASE_URL"]
+    engine = create_async_engine(db_url, echo=False)
+    app.db_sessionmaker: async_sessionmaker[AsyncSession] = async_sessionmaker(
+        engine, expire_on_commit=False
+    )
+    app._db_engine = engine

fablednetmon/models/__init__.py

@@ -0,0 +1,4 @@
+from .base import Base
+from .users import User
+
+__all__ = ["Base", "User"]

fablednetmon/models/base.py

@@ -0,0 +1,5 @@
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass

fablednetmon/models/users.py

@@ -0,0 +1,2 @@
+# fablednetmon/models/users.py — stub, filled in Task 4
+from .base import Base