feat: 数据源编辑加排除数据库+脱敏字段+审批流关联; 权限组Transfer改为选择实例

- EditInstanceDialog: 新增排除数据库(逗号分隔)、脱敏字段(动态表单+表/字段/规则)、审批流程关联
- Instance: workflow JSON字段改为workflow_id FK关联workflow_definitions表
- InstanceGroupPage: Transfer穿梭框从选数据库改为选实例(数据源)
- 后端instance API返回workflow_name, _get_workflow_names批量查询
- DB迁移: instances表添加workflow_id列
- 37个测试全部通过

backend/app/models/instance.py

@@ -22,7 +22,7 @@ class Instance(Base):
 
     # 新增字段
     access_mode = Column(String(20), default="readwrite")  # readwrite / read / write
-    workflow = Column(Text, nullable=True)  # JSON: [{stage, role, assignee}]
+    workflow_id = Column(Integer, ForeignKey("workflow_definitions.id", ondelete="SET NULL"), nullable=True)
     excluded_databases = Column(Text, nullable=True)  # JSON: ["sys", "information_schema", ...]
     mask_fields = Column(Text, nullable=True)  # JSON: [{table, field, rule}]
 
@@ -34,3 +34,4 @@ class Instance(Base):
 
     # 关系
     group = relationship("InstanceGroup", back_populates="instances")
+    workflow_def = relationship("WorkflowDefinition")