feat(models): Task/Product 模型扩充 + 4个Alembic迁移

Task 模型:
- 新增 received_at, completed_at, reject_reason, is_rework
- 新增 TaskRecord 模型 (remark + images JSON)
- 状态常量 PENDING/WIP/COMPLETED/REJECTED/ARCHIVED
- 全部时间字段改用北京时间 (get_beijing_time)

Product 模型:
- order_id → 可选; 新增 external_serial, current_location_id
- 新增 material_name/spec_model/category/material_type 快照字段
- 新增 overall_status (备货/生产/测试/维修/在库)

迁移:
- b2c3: HEX计数器Sequence + external_serial + order_id nullable
- c3d4: material快照4列
- d4e5: overall_status
- e5f6: task_records表

backend/alembic/versions/b2c3d4e5f6a7_product_hex_counter_and_material_fields.py

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+"""product hex counter + material fields + optional order
+
+Revision ID: b2c3d4e5f6a7
+Revises: a1b2c3d4e5f6
+Create Date: 2026-08-04 15:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = 'b2c3d4e5f6a7'
+down_revision: Union[str, Sequence[str], None] = 'a1b2c3d4e5f6'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # === 16进制计数器 Sequence ===
+    op.execute("CREATE SEQUENCE IF NOT EXISTS product_hex_counter START 1;")
+
+    # === products 表: order_id → 可选 ===
+    op.alter_column('products', 'order_id',
+                    existing_type=sa.UUID(),
+                    nullable=True,
+                    existing_comment='所属订单ID(可选)')
+
+    # === products 表: 新增 external_serial ===
+    op.add_column('products', sa.Column(
+        'external_serial',
+        sa.String(length=64),
+        nullable=True,
+        comment='用户自定义产品序列号(可选)',
+    ))
+
+
+def downgrade() -> None:
+    op.drop_column('products', 'external_serial')
+    op.alter_column('products', 'order_id',
+                    existing_type=sa.UUID(),
+                    nullable=False)
+    op.execute("DROP SEQUENCE IF EXISTS product_hex_counter;")

backend/alembic/versions/c3d4e5f6a7b8_add_product_material_snapshot_fields.py

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+"""add product material snapshot fields
+
+Revision ID: c3d4e5f6a7b8
+Revises: b2c3d4e5f6a7
+Create Date: 2026-08-05 10:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = 'c3d4e5f6a7b8'
+down_revision: Union[str, Sequence[str], None] = 'b2c3d4e5f6a7'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column('products', sa.Column(
+        'material_name', sa.String(length=255), nullable=True, comment='物料名称快照'))
+    op.add_column('products', sa.Column(
+        'spec_model', sa.String(length=255), nullable=True, comment='规格型号快照'))
+    op.add_column('products', sa.Column(
+        'category', sa.String(length=255), nullable=True, comment='物料分类快照'))
+    op.add_column('products', sa.Column(
+        'material_type', sa.String(length=100), nullable=True, comment='物料类型快照'))
+
+
+def downgrade() -> None:
+    op.drop_column('products', 'material_type')
+    op.drop_column('products', 'category')
+    op.drop_column('products', 'spec_model')
+    op.drop_column('products', 'material_name')

backend/alembic/versions/d4e5f6a7b8c9_add_product_overall_status.py

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+"""add product overall_status
+
+Revision ID: d4e5f6a7b8c9
+Revises: c3d4e5f6a7b8
+Create Date: 2026-08-05 12:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = 'd4e5f6a7b8c9'
+down_revision: Union[str, Sequence[str], None] = 'c3d4e5f6a7b8'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column('products', sa.Column(
+        'overall_status',
+        sa.String(length=20),
+        nullable=True,
+        comment='宏观状态: 备货/生产/测试/维修/在库',
+    ))
+
+
+def downgrade() -> None:
+    op.drop_column('products', 'overall_status')

backend/alembic/versions/e5f6a7b8c9d0_add_task_records.py

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+"""add task_records table
+
+Revision ID: e5f6a7b8c9d0
+Revises: d4e5f6a7b8c9
+Create Date: 2026-08-06 10:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+
+
+revision: str = 'e5f6a7b8c9d0'
+down_revision: Union[str, Sequence[str], None] = 'd4e5f6a7b8c9'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table('task_records',
+        sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column('task_id', UUID(as_uuid=True), sa.ForeignKey('tasks.id'), nullable=False, comment='所属任务ID'),
+        sa.Column('remark', sa.String(length=2000), nullable=True, comment='备注文本'),
+        sa.Column('images', sa.String(length=4000), nullable=True, comment='图片URL列表(JSON字符串)'),
+        sa.Column('created_at', sa.DateTime(timezone=True), nullable=False, comment='记录时间'),
+        sa.PrimaryKeyConstraint('id'),
+    )
+    op.create_index(op.f('ix_task_records_task_id'), 'task_records', ['task_id'], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f('ix_task_records_task_id'), table_name='task_records')
+    op.drop_table('task_records')