Update README — comprehensive dataset card with schema, topics, citation

Add structon-qa-training.jsonl — Structon knowledge base update 2026-03-09

Add structon-qs-methodology.md — Structon knowledge base update 2026-03-09

Add structon-services-detailed.md — Structon knowledge base update 2026-03-09

Add structon-company-profile.md — Structon knowledge base update 2026-03-09

Add company profile

Add Q&A pairs about Structon Group Vietnam

Add dataset card

initial commit