Add Google Agent CLI recipe: retail search + virtual try-on

[tanvisinghal-0105]

Summary

Production-ready retail agent recipe with:

• Semantic product search via Vertex AI Vector Search 2.0 +
  BigQuery
• Virtual try-on using virtual-try-on-001 (Imagen) and Gemini
  image models
• Product recommendations (collaborative, content-based,
  LLM-driven)
• Content generation (descriptions, SEO, marketing copy)
• Voice mode via Gemini Live API

Built on Google Cloud (Vertex AI, BigQuery, GCS) using ADK.

Test plan

• Smoke test passed
• 391 unit tests passed
• Eval quality: 100% across all 4 skills
• End-to-end tested: product search, VTO with real image generation, recommendations, content generation on ADK web UI