Fix/dashscope mulit model

[guoming]

Description

Related Issue

Type of Change

• [- ] 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📝 Documentation update
• 🔧 Refactoring (no functional changes)
• 🧪 Test update

Changes Made

• qwen3.6-plus 须走 DashScope 多模态端点；Graph 下发的 ModelRequest 里 multiModel=false 会在合并时盖掉 application.yml 的默认配置，仍走纯文本端点，从而触发官方文档中的 url error, please check url！（模型与 API 端点不匹配）。
• DashScopeMultimodalEndpointInterceptor 放在模型拦截器链最前，在 multi-model 为 true 时把请求 options 规范为 multiModel=true。

How Has This Been Tested?

• Unit tests
• Integration tests
• Manual testing

Test Configuration:

• Java Version:
• OS:

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

[canfuu]

LGTM