Documentation: Reduce docs/ by 67% - Remove outdated files

Cleaned up documentation directory by removing 29 outdated files:
- Removed ancient phase-specific docs (phases 2, 36, 115)
- Removed completed planning documents (constructors, encapsulation, LuaStack, macros)
- Removed duplicate files (docs/claude.md, STATUS_UPDATE, ROADMAP)
- Removed outdated analyses (lvm, lambda, loops, allocators, unions)

Updated remaining files:
- SPAN_MODERNIZATION_PLAN.md: Added Phase 115-116 status update
- TYPE_MODERNIZATION_ANALYSIS.md: Updated to reflect Phases 114-119 completion

Result:
- Before: 38 files, 25,043 lines
- After: 10 files, 8,280 lines
- Reduction: 67% fewer files, 67% fewer lines

Remaining essential documentation:
- CMAKE_BUILD.md (87 lines)
- COVERAGE_ANALYSIS.md (374 lines)
- REFACTORING_SUMMARY.md (452 lines)
- CPP_MODERNIZATION_ANALYSIS.md (953 lines)
- TYPE_MODERNIZATION_ANALYSIS.md (953 lines)
- GC_PITFALLS_ANALYSIS.md (995 lines)
- GC_SIMPLIFICATION_ANALYSIS.md (1,008 lines)
- SRP_ANALYSIS.md (1,008 lines)
- UNDEFINED_BEHAVIOR_ANALYSIS.md (1,179 lines)
- SPAN_MODERNIZATION_PLAN.md (1,271 lines)

All remaining docs are actively referenced in CLAUDE.md's Documentation Index.

Author: claude