[BUGFIX] SHALL/MUST should be in body not in the requirement title

bug:

✗ [ERROR] agent-management/spec.md: MODIFIED "系统 SHALL 支持为 Box 智能体配置 Prompt Caching 开关" must contain SHALL or MUST


my spec:

```
## MODIFIED Requirements

### Requirement:  系统 SHALL 支持为 Box 智能体配置 Prompt Caching 开关
HOW TO DO ? NO CMD(S H A L L /  M U S T) HERE


```

LLM may set SHALL to Requirement title, so we should let llm to set SHALL to the body not Requirement title