Polish Sema paper tightening

[hwesterb]

Summary

• Tighten the Sema paper refinement section around the versioned design manual and audit discipline
• Compress the Creative Discovery Loop's candidate-source paragraph
• Clarify contribution taxonomy for C6/C7
• Regenerate the paper PDF via the compile script

Validation

• ./scripts/compile_paper.sh (36 pages, 0 undefined references)

Note

• Local pre-commit pytest under system Python 3.9 fails during collection on Python 3.10 union type syntax in existing code; this is unrelated to the paper-only change.