feat: 产品协同留言板 — ProductMessage 模型 + API + 迁移

- 新增 ProductMessage 模型，挂载在 products.id（ON DELETE CASCADE）
- GET/POST /products/{id}/messages 接口
- 注册到 Alembic 自动发现

backend/alembic/versions/g1h2i3j4k5l6_add_product_messages.py

@@ -0,0 +1,33 @@
+"""add_product_messages
+
+Revision ID: g1h2i3j4k5l6
+Revises: c9d0e1f2a3b4
+Create Date: 2026-08-10
+
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision: str = "g1h2i3j4k5l6"
+down_revision: Union[str, None] = "c9d0e1f2a3b4"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "product_messages",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("product_id", postgresql.UUID(as_uuid=True),
+                  sa.ForeignKey("products.id", ondelete="CASCADE"),
+                  index=True, nullable=False),
+        sa.Column("operator_id", sa.String(50), nullable=False),
+        sa.Column("content", sa.Text, nullable=False),
+        sa.Column("created_at", sa.DateTime, nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("product_messages")

backend/app/models/__init__.py

@@ -6,6 +6,7 @@ from app.models.task import Task, TaskRecord
 from app.models.task_log import TaskLog
 from app.models.notification import Notification
 from app.models.app_version import AppVersion
+from app.models.message import ProductMessage
 __all__ = [
     "Base",
     "ProductionOrder",
@@ -15,4 +16,5 @@ __all__ = [
     "TaskLog",
     "Notification",
     "AppVersion",
+    "ProductMessage",
 ]

backend/app/models/message.py

@@ -0,0 +1,32 @@
+"""产品协同留言板模型"""
+import uuid
+from datetime import datetime
+from sqlalchemy import String, Text, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.models.base import Base
+
+
+class ProductMessage(Base):
+    __tablename__ = "product_messages"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4,
+    )
+    product_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("products.id", ondelete="CASCADE"),
+        index=True,
+        nullable=False,
+        comment="所属产品 ID",
+    )
+    operator_id: Mapped[str] = mapped_column(
+        String(50), nullable=False, comment="留言人姓名或工号",
+    )
+    content: Mapped[str] = mapped_column(
+        Text, nullable=False, comment="留言内容",
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, default=datetime.utcnow, comment="留言时间",
+    )