Align README with current API

[SonAIengine]

Summary

• align English/Korean root READMEs with the current public API and deterministic default path
• add infrastructure integration guidance for PostgreSQL, Kuzu, Qdrant, MinIO, dependency extras, and scale-out composition
• remove stale root README version notes, legacy engine guidance, and historical fixed benchmark tables
• document current memory operating layer usage and move benchmark numbers to versioned reports

Verification

• uv run ruff check .
• uv run synaptic-quickstart --json
• memory operating layer example import/search/feedback/health smoke