Set CRM order status to PACKED after Checkbox accepts the receipt

- ExoCrmClient.set_status: live SetStatus needs {Orders: [id], Status} and
  replies per order, unlike the documented {ID, Status}
- receipts.crm_status_set_at (migration 0006); set right after creation,
  retried by cron, row-locked to avoid a repeat PACKED overwriting a newer status
- CRM errors under capitalized 'Errors' and non-JSON replies are reported

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/alembic/versions/0006_receipt_crm_status_set_at.py

@@ -0,0 +1,28 @@
+"""Отметка о смене статуса заказа в CRM после создания чека
+
+Revision ID: 0006
+Revises: 0005
+Create Date: 2026-09-24
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0006"
+down_revision: str | None = "0005"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "receipts", sa.Column("crm_status_set_at", sa.DateTime(timezone=True), nullable=True)
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("receipts", "crm_status_set_at")