fix(config): accept allowAgents in agent list

[ailuntz]

Summary

• honor top-level allowAgents in openclaw.json agent entries
• keep subagents.allowAgents as fallback
• add regression test for allowAgents

Testing

• not run (script + test only)

Fixes #104

[cft0808]

代码审查通过 ✅

修复 openclaw.json 中 allowAgents 既可在顶层也可在 subagents 下的兼容问题。附带回归测试。修复 #104。建议合并。