docs: add blog on VLLM semantic router + Milvus integration

[yinmin2020]

What type of PR is this?
docs(website): add blog post about semantic routing with VLLM and Milvus

What this PR does / why we need it:
This PR adds a new blog post that introduces how to build a semantic routing layer using VLLM and Milvus. The article covers:

• The motivation behind semantic routing
• Architecture overview with mixture of models
• Step-by-step guide to set up the system using Docker Compose
• How semantic caching can improve performance and reduce costs
• Integration with Milvus for vector storage and retrieval

This content helps users understand advanced use cases of the project and demonstrates practical integration with popular LLM and vector database tools.

Which issue(s) this PR fixes:
None

Release Notes: No

[netlify]

❌ Deploy Preview for vllm-semantic-router failed.

Name	Link
🔨 Latest commit	e77c27d
🔍 Latest deploy log	https://app.netlify.com/projects/vllm-semantic-router/deploys/6904ac7573e15800071af78b

[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 website

Owners: @Xunzhuo, @rootfs, @yuluo-yx
Files changed:

• website/blog/2025-10-30-milvus.md
• website/static/img/docker-compose-up.png
• website/static/img/docker-compose.png
• website/static/img/download-models.png
• website/static/img/mixture-of-models.png
• website/static/img/semantic-caching-challenge.png
• website/static/img/semantic-routing-layer.png
• website/static/img/traditional-caching.png

---

🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

[rootfs]

@yinmin2020 thank you for the contribution! can you sign the DCO and fix the CI issues?