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.

pyproject.toml

@@ -42,11 +42,10 @@ exclude = [".venv", "venv", "migrations", "docs"]
 #   RET          return-flow tidiness
 #   SIM          obvious simplifications
 #   UP           syntax available on the 3.12 this targets
-#
-# isort (I) is not enabled yet: it would reorder imports in 48 files, i.e. a
-# second sweep of pure churn right after the formatting commit. Worth doing,
-# worth doing on its own.
-select = ["E4", "E7", "E9", "F", "B", "C4", "RET", "SIM", "UP"]
+#   I            isort; enabled in its own commit, for the same reason the
+#                formatting got one — the diff is churn and must not hide
+#                behind a behavioural change
+select = ["E4", "E7", "E9", "F", "B", "C4", "RET", "SIM", "UP", "I"]
 
 # Forcing a ternary reads worse than the if/else it replaces in the one place
 # it fires (evaluations.py, choosing a sort direction).
@@ -56,7 +55,14 @@ ignore = ["SIM108"]
 # Intentional re-export facade: `from app.models import User, Tryout, ...`
 # is the documented entry point, and importing the modules is what
 # registers every model with SQLAlchemy.
-"app/models/__init__.py" = ["F401"]
+#
+# I001 is off here too. The imports are grouped into eleven commented
+# layers that spell out the dependency graph (constants → users → teams →
+# tryouts → matches → participants). Alphabetising them leaves every
+# heading above an import it does not describe, and the file's one job is
+# to be read. The order is documentation, not a requirement: the suite
+# passes either way.
+"app/models/__init__.py" = ["F401", "I001"]
 "app/models/user_model/__init__.py" = ["F401"]
 "tests/conftest.py" = ["E402"]