🚀 Start Phase 15.3: Nyash compiler MVP implementation

Major milestone:
- Set up apps/selfhost-compiler/ directory structure
- Implement basic Nyash compiler in Nyash (CompilerBox)
- Stage-1: Basic arithmetic parser (int/string/+/-/*/括弧/return)
- JSON v0 output compatible with --ny-parser-pipe
- Runner integration with NYASH_USE_NY_COMPILER=1 flag
- Comprehensive smoke tests for PHI/Bridge/Stage-2

Technical updates:
- Updated CLAUDE.md with Phase 15.3 status and MIR14 details
- Statement separation policy: newline-based with minimal ASI
- Fixed runaway ny-parser-pipe processes (CPU 94.9%)
- Clarified MIR14 as canonical instruction set (not 13/18)
- LoopForm strategy: PHI auto-generation during reverse lowering

Collaborative development:
- ChatGPT5 implementing compiler skeleton
- Codex provided LoopForm PHI generation guidance
- Claude maintaining documentation and coordination

🎉 セルフホスティングの歴史的一歩！自分自身をコンパイルする日が近いにゃ！

Co-Authored-By: ChatGPT <noreply@openai.com>

docs/reference/language/README.md

@@ -10,6 +10,9 @@ This is the entry point for Nyash language documentation.
 - Sugar Transformations (?., ??, |> and friends): parser/sugar.rs (source) and tools/nyfmt/NYFMT_POC_ROADMAP.md
 - Peek Expression Design/Usage: covered in the Language Reference and Phase 12.7 specs above
 
+Statement separation and semicolons
+- See: reference/language/statements.md — newline as primary separator; semicolons optional for multiple statements on one line; minimal ASI rules.
+
 Related implementation notes
 - Tokenizer: src/tokenizer.rs
 - Parser (expressions/statements): src/parser/expressions.rs, src/parser/statements.rs