Add research papers to Official Library

[suguanYang]

Summary

• Add five Research papers entries to the Official Library catalog
• Add ready text-only demo bundles for the new PDFs so they can be materialized without a parser job
• Cover the new ready research sources in the demo catalog contract test

Documents

• Attention Is All You Need
• Retrieval-Augmented Generation for Large Language Models: A Survey
• Retrieval-Augmented Generation Realized
• Toolformer: Language Models Can Teach Themselves to Use Tools
• AI Agents Overview

Verification

• S3_BUCKET_NAME=local S3_ACCESS_KEY_ID=local S3_SECRET_ACCESS_KEY=local S3_TEMP_PATH=/tmp DATABASE_URL=sqlite:///tmp.db TMP_PATH=/tmp uv run --project apps/api pytest apps/api/tests/contract/test_demo_documents_contract.py -q
• uv run --group lint ruff check apps/api/app/services/demo/official_library_catalog.py apps/api/app/services/demo/source_catalog.py apps/api/tests/contract/test_demo_documents_contract.py
• uv run pyright apps/api/app/services/demo/official_library_catalog.py apps/api/app/services/demo/source_catalog.py apps/api/tests/contract/test_demo_documents_contract.py
• make lint
• make typecheck
• git diff --check

Note: full apps/api/scripts/validate_demo_documents.py currently reports pre-existing stale doc_nav.json files for older demo documents on main; the new research bundles were generated with fresh doc_nav.json and did not appear in that failure list.