feat(phase7.4): order rejection + resubmit flow

- Migration 053: rejection_reason TEXT NULL on orders table
- POST /api/orders/{id}/reject (PM+): sets rejected status, cancels
  active renders, stores reason, notifies creator, broadcasts WS event
- POST /api/orders/{id}/resubmit (creator or PM+): resets to draft,
  clears rejection fields, notifies PMs
- OrderDetail: Reject button (PM+) + inline modal with reason textarea
  and notify-client checkbox; Resubmit button; rejection reason amber
  alert box shown below header when order is rejected
- Orders Kanban: rejection_reason shown as red italic note on card
- Order interface: rejected_at, rejection_reason fields

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/alembic/versions/053_order_rejection.py

@@ -0,0 +1,26 @@
+"""Add rejection_reason to orders table.
+
+Revision ID: 053
+Revises: 052
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.engine.reflection import Inspector
+
+revision = "053"
+down_revision = "052"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    inspector = Inspector.from_engine(bind)
+    columns = [c["name"] for c in inspector.get_columns("orders")]
+
+    if "rejection_reason" not in columns:
+        op.add_column("orders", sa.Column("rejection_reason", sa.Text(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("orders", "rejection_reason")