chore(lint): trier les imports, sauf la facade des modeles

Active la regle isort (I) de ruff. 45 fichiers reordonnes, aucun
changement de comportement : la suite passe avant comme apres.

app/models/__init__.py en est exclu. Ses imports sont ranges en onze
couches commentees qui decrivent le graphe de dependances ; trier par
ordre alphabetique laisse chaque titre au-dessus d un import qu il ne
decrit pas, et ce fichier n a qu un role, etre lu.

Commit isole, comme le formatage : un diff de brassage ne doit pas
servir de couverture a un changement de comportement.

app/routes/users/__init__.py

@@ -9,16 +9,16 @@ keeps its single `from app.routes.users import users_bp`. The blueprint
 itself lives in blueprint.py to keep that import one-directional.
 """
 
-from app.routes.users.blueprint import users_bp
-
 # Imported for their side effect: each module attaches its routes to
 # users_bp. Order does not matter; none of them import each other.
-from app.routes.users import accounts  # noqa: F401,E402
-from app.routes.users import availability  # noqa: F401,E402
-from app.routes.users import contracts  # noqa: F401,E402
-from app.routes.users import notes  # noqa: F401,E402
-from app.routes.users import one_on_one  # noqa: F401,E402
-from app.routes.users import profile  # noqa: F401,E402
+from app.routes.users import (
+    accounts,  # noqa: F401,E402
+    availability,  # noqa: F401,E402
+    contracts,  # noqa: F401,E402
+    notes,  # noqa: F401,E402
+    one_on_one,  # noqa: F401,E402
+    profile,  # noqa: F401,E402
+)
 
 # Re-exported because tests and other modules reach for them by name.
 from app.routes.users._shared import (  # noqa: F401,E402
@@ -26,6 +26,7 @@ from app.routes.users._shared import (  # noqa: F401,E402
     ALLOWED_SIGNED_EXTENSIONS,
     pdf_upload_error,
 )
+from app.routes.users.blueprint import users_bp
 
 __all__ = [
     'ALLOWED_CONTRACT_EXTENSIONS',