feat(notification): 通知标题和正文支持多语言

- 通知静态配置支持 title/body i18n
- 前端通知列表和详情页展示本地化内容
- 新增数据库迁移脚本
- 更新通知协议文档

backend/src/models/notification.py

@@ -3,12 +3,12 @@ from __future__ import annotations
 import uuid
 from datetime import datetime
 
-from sqlalchemy import CheckConstraint, DateTime, Index, String, Text, text
+from sqlalchemy import CheckConstraint, DateTime, Index, String, text
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
 from core.db.base import Base, SoftDeleteMixin, TimestampMixin
-from core.db.types import json_jsonb
+from core.db.types import json_jsonb as jsonb
 from schemas.enums import NotificationTargetMode
 
 
@@ -57,10 +57,14 @@ class Notification(TimestampMixin, SoftDeleteMixin, Base):
     source_key: Mapped[str | None] = mapped_column(String(128), nullable=True)
     source_version: Mapped[int | None] = mapped_column(nullable=True)
     content_hash: Mapped[str | None] = mapped_column(String(64), nullable=True)
-    title: Mapped[str] = mapped_column(Text, nullable=False)
-    body: Mapped[str] = mapped_column(Text, nullable=False)
+    title: Mapped[dict[str, str]] = mapped_column(
+        jsonb, nullable=False, server_default=text("'{}'::jsonb"), default=dict,
+    )
+    body: Mapped[dict[str, str]] = mapped_column(
+        jsonb, nullable=False, server_default=text("'{}'::jsonb"), default=dict,
+    )
     payload: Mapped[dict[str, object]] = mapped_column(
-        json_jsonb,
+        jsonb,
         nullable=False,
         server_default=text("'{}'::jsonb"),
         default=dict,