chore: archive old session docs and clean workspace

Workspace cleanup:
- Moved 10 session docs to ../archive/loamSpine-session-dec-26-2025/
- Archived: session reports, phase completions, and interim docs
- Kept current: README, STATUS, DOCS_INDEX, and active planning docs
- Ran cargo clean to remove build artifacts

Remaining root docs (production-ready):
- README.md, STATUS.md, DOCS_INDEX.md
- CONTINUOUS_IMPROVEMENT_COMPLETE.md (latest summary)
- SESSION_INDEX.md (navigation guide)
- COMPREHENSIVE_AUDIT_DEC_26_2025.md (reference)
- HARDCODING_ELIMINATION_PLAN.md, HARDCODING_STATUS.md
- INTEGRATION_GAPS.md, CONTRIBUTING.md, etc.

Clean workspace ready for continued development.

Author: BiomeOS Developer