docs: document llm-d Kubernetes deployment

[franciscojavierarceo]

Summary

• document how to connect Agentic API to an llm-d Router in Kubernetes, including topology, readiness checks, rollout behavior, and model-server sizing
• capture the validated CoreWeave Qwen3-8B/H100 smoke-test profile and mutable-image-tag deployment lesson
• update the You.com Search API endpoint and add secure secret setup, smoke testing, and 403 troubleshooting guidance

Test Plan

• Build the MkDocs site with strict validation
• Run pre-commit hooks against both changed documentation files
• Run git diff whitespace/error checks