feat: 修复 H5 底部导航覆盖 + 更新项目进度文档

## H5 底部导航修复 (Bug #10)
- 精简 App.vue，移除重复 tabbar，仅保留全局样式
- uni-page 设置 height: calc(100% - 50px) + overflow-y: auto
- 内容区域精确停在底部导航上方，独立滚动不再叠加
- 恢复 custom-tab-bar 组件

## 项目进度文档
- PROGRESS.md 更新至 10 个 Bug 修复
- 新增 H5 底部导航修复记录
- 新增历史变更条目

backend/app/models/notification.py

@@ -0,0 +1,20 @@
+from sqlalchemy import Column, String, Boolean, DateTime, Text, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from datetime import datetime
+from app.database import Base
+import uuid
+
+
+class Notification(Base):
+    __tablename__ = "notifications"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), nullable=False, index=True)
+    title = Column(String(255), nullable=False)
+    content = Column(Text, nullable=False)
+    notification_type = Column(String(50), default="system")
+    reference_type = Column(String(50))
+    reference_id = Column(String(255))
+    is_read = Column(Boolean, default=False)
+    notify_metadata = Column("metadata", JSONB, default={})
+    created_at = Column(DateTime, default=datetime.utcnow)