docs: add comprehensive enhancement suite status tracking

Documents implementation status of 5 optional enhancements:

1. ✅ Debugger Support (Phase 1 complete: source maps + mode metadata)
   - Phases 2-4 planned (DWARF, DAP, VS Code integration)

2. ⏳ Package Manager (not started)
   - Cargo-style dependency management
   - Module import syntax
   - Local registry

3. ⏳ Performance Benchmarks (not started)
   - Ephapax vs Rust vs AssemblyScript
   - Compilation speed, binary size, runtime perf
   - CI integration

4. ⏳ VS Code Extension (not started)
   - Syntax highlighting
   - LSP integration (reuse existing ephapax-lsp)
   - Mode switcher UI

5. ⏳ Closure Environment Optimization (not started)
   - Escape analysis + free variable analysis
   - Minimal capture sets
   - 10-30% binary size reduction expected

Overall completion: 20% (1/5 done)

Recommended implementation order: #2 → #3 → #4 → #5 → #1 (complete)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell