feat: database setup with SQLAlchemy ORM models for Device and DeviceLog

- Replace minimal database.py with full SQLAlchemy async setup
- Create Device and DeviceLog models with proper relationships
- Add tests for model creation and relationship functionality
- Fixed lazy loading issue in tests by avoiding .count() on dynamic relationships

src/mqtt_home/database.py

@@ -1,5 +1,33 @@
+from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, async_session
 from sqlalchemy.orm import DeclarativeBase
+from mqtt_home.config import get_settings
 
 
 class Base(DeclarativeBase):
-    pass
+    pass
+
+
+def get_engine():
+    settings = get_settings()
+    return create_async_engine(
+        settings.database_url,
+        echo=False,
+    )
+
+
+def get_session_factory(engine=None):
+    _engine = engine or get_engine()
+    return async_sessionmaker(_engine, expire_on_commit=False)
+
+
+async def init_db():
+    engine = get_engine()
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    await engine.dispose()
+
+
+async def get_db():
+    factory = get_session_factory()
+    async with factory() as session:
+        yield session