Fix ruff lint errors across codebase

- Auto-fix F401 (unused imports) and I001 (unsorted imports) with ruff --fix
- Manually fix E501 (line too long) in alembic migrations and src/ models
- Run ruff format to ensure consistent formatting

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/test_config.py

@@ -28,7 +28,10 @@ def test_database_url_normalizes_plain_postgresql_prefix():
         "DATABASE_URL": "postgresql://cartsnitch:cartsnitch@localhost:5432/cartsnitch",
     }
     settings = Settings(**env)
-    assert settings.database_url == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    assert (
+        settings.database_url
+        == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    )
 
 
 def test_database_url_preserves_asyncpg_prefix():
@@ -37,10 +40,16 @@ def test_database_url_preserves_asyncpg_prefix():
         "CARTSNITCH_DATABASE_URL": "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch",
     }
     settings = Settings(**env)
-    assert settings.database_url == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    assert (
+        settings.database_url
+        == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    )
 
 
 def test_database_url_default():
     """When neither env var is set, the hardcoded default is used."""
     settings = Settings()
-    assert settings.database_url == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    assert (
+        settings.database_url
+        == "postgresql+asyncpg://cartsnitch:cartsnitch@localhost:5432/cartsnitch"
+    )