Restructure volumes 2-3, rewrite placeholders, polish titles and metadata

Structure changes:
- Ch04: merge 04d+04d1 (memory+handoff), merge 04e+04f into conclusion
- Ch05: compress 05c1-05c6 into single 05c, merge 05d into conclusion
- Ch06: simplify to 3 sub-chapters, Conway/principles into conclusion
- Ch07: new chapter for role redefinition (was scattered across 06)
- Archive 48 old draft files to archive/old-drafts/

Content improvements:
- Rewrite all v2/v3 placeholders as substantive prose (not templates)
- Unify volume numbers (1→10x, 10→100x) across SUMMARY and README
- Fix chapter titles to follow "concept: what it solves" pattern
- Rename introduction to "为什么需要 Harness Engineering"
- Update README status from "early draft/architecture validation" to
  "Part I has first draft, Parts II-III in development"
- Update contributors page with contact info
- Add explicit README entry in SUMMARY for proper HonKit navigation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fqzz2000