feat: v0.21.0 Connector Expansion + Multimodal + Observability

[johnnichev]

Summary

• 3 new vector stores: FAISS, Qdrant, pgvector with full CRUD + metadata filtering
• Azure OpenAI provider: extends OpenAI provider with Azure endpoint support
• Multimodal messages: ContentPart dataclass, image_message(), text_content() helpers
• OTel + Langfuse observers: OpenTelemetry GenAI spans + Langfuse trace export
• 4 document loaders: CSV, JSON, HTML, URL (from_csv, from_json, from_html, from_url)
• 4 new toolbox categories (9 tools): code execution, web search, GitHub, database query
• 12 new examples (77-88) + 4 notebook steps
• Live simulation viewer at /simulations/ with pre-recorded agent traces
• Examples gallery with 88 examples + 10 simulations
• 306 new tests across all new modules
• Docs: updated RAG, Toolbox, Providers, Streaming, Quickstart, llms.txt, mkdocs.yml
• Feature skill + CLAUDE.md: documentation updates now mandatory (Step 7a-7e)

Test plan

• pytest tests/ -x -q — all 4612 tests pass
• New vector store tests (FAISS, Qdrant, pgvector) — 181 tests
• Document loader tests — 46 tests
• Toolbox tests (code, search, GitHub, DB) — 89 tests
• Observer tests (OTel, Langfuse) — 25 tests
• Multimodal message tests — 19 tests
• mkdocs build — docs build clean