Document infrastructure integration options

[SonAIengine]

Summary

• add English/Korean README guidance for PostgreSQL, Kuzu, Qdrant, MinIO, and CompositeBackend
• expand install extras so users can choose database, vector, blob, scale, and RAG dependencies deliberately
• clarify that Qdrant and MinIO are helper services behind CompositeBackend, not standalone graph stores
• call out the surrounding operating-layer needs for multi-terabyte production corpora

Verification

• uv run ruff check .
• git diff --check
• stale README pattern scan