Add WFGY Core 2.0 system prompt and 60s self test

[onestardao]

Summary

• Add a new system prompt file for WFGY Core 2.0 in SystemPrompts/Misc/20260223-WFGY-Core2.md.
• The file contains:
  • a math-based “stable reasoning” system prompt that can be used with any strong LLM
  • a small 60s self-test prompt to quickly compare A/B/C modes (no-core vs silent-core vs explicit-core).
• Update SystemPrompts/README.md Miscellaneous section with a new entry:
  • “WFGY Core 2.0 – Stable reasoning system prompt – 02/23/2026”.

Test plan

• Confirmed the new file is placed under SystemPrompts/Misc/ and follows the existing naming convention (YYYYMMDD-Name.md).
• Checked that the markdown renders correctly (title, short description, fenced code blocks for the system prompt and the self-test).
• Verified the Miscellaneous list in SystemPrompts/README.md links correctly to SystemPrompts/Misc/20260223-WFGY-Core2.md.
• No changes made to existing system prompt contents.