Docs:
- CLAUDE.md: replace inaccurate "frontend codebase is not opensourced"
  with the explicit "frontend source code is not in this public
  repository" callout used in .github/copilot-instructions.md; update
  compose service list to nginx/frontend/backend/core/mysql/redis/kafka/
  seaweedfs/qdrant.
- README.md: change "three core roles" to "four core roles" (add
  Developer, aligning with docs/overview.md); expand compose service
  list to the full set; fix repo casing microsoft/sico -> microsoft/Sico;
  add "local development only" note next to the seeded operator
  credentials.
- docs/quickstart.md, docs/roadmap.md, .github/ISSUE_TEMPLATE/config.yml,
  examples/knowledge/create_link_document.py: fix repo casing
  microsoft/sico -> microsoft/Sico; add the same "local dev only" note
  to quickstart's seeded account section.
- SECURITY.md: add MSRC (msrc.microsoft.com / secure@microsoft.com) as
  the preferred reporting channel; keep GitHub PVR as an alternative
  and leave the rest of the policy untouched.

Core hygiene:
- core/app/biz/chat/service.py: remove stray print(prompt) debug line.
- core/README.md: delete obsolete top-level README (no docs link here).