refactor: simplify create-expert — remove plan, must/should signals, direct delegation

[FL4TLiN3]

Summary

Major simplification of create-expert pipeline (346→171 lines):

• Remove plan expert — write handles planning + authoring, produces perstack.toml + test-spec.md
• Flatten delegation — write delegates to review directly (soft signal as direct delegation pattern)
• Simplify names — write, review, test, verify (drop -definition, -expert, -test suffixes)
• Hard signal redesign:
  • Must: ONE signal, binary, core task completion. Always blocks sign-off.
  • Should: multiple signals, user value checks, threshold-based sign-off (e.g., "≤ N of M fail")
• Remove domain knowledge principles — focus on signal design over task decomposition
• Soft signal pattern — executors delegate to reviewers directly (recommended for generated experts too)

Structure

Before: create-expert → {plan, write-definition, review-definition, test-expert, verify-test}
After:  create-expert → {write → review, test, verify}

Test plan

• Run create-expert and verify write produces both perstack.toml and test-spec.md
• Verify test-spec.md has exactly ONE must signal and multiple should signals with threshold
• Confirm verify only CONTINUEs on must signal failure
• Check write delegates to review and addresses feedback before returning

🤖 Generated with Claude Code