docs: archive implementation and working documents

Phase 3 (Migration & Cleanup) - Archive Phase Complete

Moved 24 implementation and working documents to doc/.archive/:

1. doc/.archive/phase1/ (3 files)
   - PHASE1_ISSUE_NUMPY_CONFLICT.md
   - PHASE1_READY_FOR_TESTING.md
   - PHASE1_TESTING_GUIDE.md

2. doc/.archive/phase2/ (10 files)
   - PHASE2_DAY1_SUMMARY.md
   - PHASE2_DAY2_SUMMARY.md
   - PHASE2_IMPLEMENTATION_PLAN.md
   - PHASE2_PROGRESS.md
   - PHASE2_TASK4_COMPLETION.md
   - PHASE2_TASK5_COMPLETE.md
   - PHASE2_TASK6_COMPLETION_SUMMARY.md
   - PHASE2_TASK6_FINAL_REPORT.md
   - PHASE2_TASK6_INTEGRATION_TESTING.md
   - PHASE2_TASK7_PLAN.md
   - PHASE2_TASK7_PROGRESS.md

3. doc/.archive/implementation-reports/ (5 files)
   - TASK4_DOCUMENTAGENT_SUMMARY.md
   - TASK6_INITIAL_RESULTS.md
   - TASK6_QUICK_WINS_COMPLETE.md
   - TASK7_INTEGRATION_COMPLETE.md
   - TASK7_RESULTS_COMPARISON.md

4. doc/.archive/working-docs/ (6 files)
   - DOCUMENTATION_CLEANUP_PLAN.md
   - FIX_DUPLICATE_COMMITS.md
   - PUSH_DECISION.md
   - PUSH_SUCCESS.md
   - TEST_RUN_SUMMARY.md
   - Various *_SUMMARY.md files

All historical implementation documents preserved in archive.
Root directory now clean and organized.

Author: vinod0m