Bénévole : retrait de la taille de t-shirt et du régime alimentaire

Champs `tshirt_size` et `diet` supprimés du modèle `Volunteer`, des schémas
d'API, de l'import CSV/Excel (mapping, suggestions, exécution) et du jeu de
démonstration. Énum `TshirtSize` et helper `parse_tshirt_size` supprimés.
Migration 0005. Clé i18n `import.row.invalid_tshirt_size` retirée.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017uUsRg7XzopkCPWimwg9ZM

backend/app/migrations/versions/0005_drop_volunteer_tshirt_diet.py

@@ -0,0 +1,38 @@
+"""Bénévole : retrait de tshirt_size et diet
+
+Revision ID: 0005_drop_volunteer_tshirt_diet
+Revises: 0004_shift_day_part
+Create Date: 2026-09-10
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0005_drop_volunteer_tshirt_diet"
+down_revision: str | None = "0004_shift_day_part"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+_TSHIRT_SIZE = sa.Enum(
+    "XS", "S", "M", "L", "XL", "XXL", "XXXL",
+    name="tshirtsize", native_enum=False,
+)
+
+
+def upgrade() -> None:
+    op.drop_column("volunteer", "tshirt_size")
+    op.drop_column("volunteer", "diet")
+
+
+def downgrade() -> None:
+    op.add_column(
+        "volunteer", sa.Column("diet", sa.String(), nullable=True)
+    )
+    op.add_column(
+        "volunteer",
+        sa.Column("tshirt_size", _TSHIRT_SIZE, nullable=True),
+    )