feat: 实现站内通知系统

- 后端: 新增 notifications/user_notifications 表迁移及 ORM 模型
- 后端: 实现 schema/repository/service/router 全套通知 API
  - GET /api/v1/notifications (列表+游标分页)
  - GET /api/v1/notifications/unread-count
  - PATCH /api/v1/notifications/{id}/read (幂等)
  - PATCH /api/v1/notifications/mark-all-read (幂等)
- 后端: payload 使用 Pydantic discriminated union (none/open_route/open_url)
- 后端: 19 个单元测试全部通过
- Flutter: 通知 feature 完整实现 (models/apis/repositories/bloc/UI)
- Flutter: Home 页通知按钮接入真实页面，显示未读 badge
- Flutter: 14 个测试全部通过
- 协议文档: notification-inbox-protocol.md 及错误码注册

backend/src/models/__init__.py

@@ -10,7 +10,9 @@ from .points_audit_ledger import PointsAuditLedger
 from .points_ledger import PointsLedger
 from .profile import Profile
 from .register_bonus_claims import RegisterBonusClaims
+from .notification import Notification
 from .system_agents import SystemAgents
+from .user_notification import UserNotification
 from .user_points import UserPoints
 
 __all__ = [
@@ -20,10 +22,12 @@ __all__ = [
     "InviteCode",
     "Llm",
     "LlmFactory",
+    "Notification",
     "PointsAuditLedger",
     "PointsLedger",
     "Profile",
     "RegisterBonusClaims",
     "SystemAgents",
+    "UserNotification",
     "UserPoints",
 ]

backend/src/models/notification.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import CheckConstraint, DateTime, Index, String, Text, 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
+
+
+class Notification(TimestampMixin, SoftDeleteMixin, Base):
+    __tablename__ = "notifications"
+    __table_args__ = (
+        CheckConstraint(
+            "status IN ('draft', 'published', 'revoked')",
+            name="ck_notifications_status",
+        ),
+        CheckConstraint(
+            "jsonb_typeof(payload) = 'object'",
+            name="ck_notifications_payload_object",
+        ),
+        Index(
+            "ix_notifications_status_created_at",
+            "status",
+            "created_at",
+        ),
+        Index(
+            "ix_notifications_published_at",
+            "published_at",
+        ),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    type: Mapped[str] = mapped_column(
+        String(32), nullable=False, server_default=text("'system'")
+    )
+    title: Mapped[str] = mapped_column(Text, nullable=False)
+    body: Mapped[str] = mapped_column(Text, nullable=False)
+    payload: Mapped[dict[str, object]] = mapped_column(
+        json_jsonb,
+        nullable=False,
+        server_default=text("'{}'::jsonb"),
+        default=dict,
+    )
+    status: Mapped[str] = mapped_column(
+        String(16), nullable=False, server_default=text("'published'")
+    )
+    published_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    revoked_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )

backend/src/models/user_notification.py

@@ -0,0 +1,41 @@
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, UniqueConstraint, text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from core.db.base import Base, TimestampMixin
+
+
+class UserNotification(TimestampMixin, Base):
+    __tablename__ = "user_notifications"
+    __table_args__ = (
+        UniqueConstraint(
+            "user_id",
+            "notification_id",
+            name="uq_user_notifications_user_notification",
+        ),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("auth.users.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    notification_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("notifications.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    is_read: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, server_default=text("false")
+    )
+    read_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )