Stabilize staff concurrency and premium emoji; enable verified Drone deployment

migrations/versions/20260913_staff_concurrency.py

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+"""Merge legacy heads, add cashiers, prevent duplicate entries and prize places."""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "20260913_staff_concurrency"
+down_revision = ("20260701_perf_indexes", "41aae82e631b")
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    connection = op.get_bind()
+    # Stop safely on ambiguous historical results; never silently delete prizes.
+    checks = (
+        ("participations", "lottery_id, account_number", "account_number IS NOT NULL"),
+        ("participations", "lottery_id, user_id", "account_number IS NULL AND user_id IS NOT NULL"),
+        ("winners", "lottery_id, place", "1=1"),
+    )
+    for table, columns, predicate in checks:
+        duplicate = connection.execute(sa.text(
+            f"SELECT 1 FROM {table} WHERE {predicate} GROUP BY {columns} HAVING COUNT(*) > 1 LIMIT 1"
+        )).first()
+        if duplicate:
+            raise RuntimeError(f"Duplicate {table} ({columns}); review duplicates before migrating. No data removed.")
+    op.add_column("users", sa.Column("is_cashier", sa.Boolean(), server_default=sa.false(), nullable=False))
+    with op.batch_alter_table("participations") as batch:
+        batch.create_unique_constraint("uq_participation_account", ["lottery_id", "account_number"])
+    op.create_index("uq_participation_user", "participations", ["lottery_id", "user_id"], unique=True,
+                    postgresql_where=sa.text("account_number IS NULL"), sqlite_where=sa.text("account_number IS NULL"))
+    with op.batch_alter_table("winners") as batch:
+        batch.create_unique_constraint("uq_winner_place", ["lottery_id", "place"])
+
+
+def downgrade():
+    with op.batch_alter_table("winners") as batch:
+        batch.drop_constraint("uq_winner_place", type_="unique")
+    op.drop_index("uq_participation_user", table_name="participations")
+    with op.batch_alter_table("participations") as batch:
+        batch.drop_constraint("uq_participation_account", type_="unique")
+    op.drop_column("users", "is_cashier")