Initialize Cm project with HIR-aware compiler architecture

[Copilot]

Cb language lacked HIR (High-level Intermediate Representation) in its design, limiting optimization and extensibility. This initializes Cm as a ground-up redesign with a modern compiler architecture.

Changes

• Project structure following standard compiler layering:

  • src/frontend/ - lexer, parser, AST
  • src/middle/ - HIR, type checking, lowering
  • src/backend/ - interpreter (initial target)

• Design documentation:

  • docs/design/architecture.md - compilation pipeline and phase responsibilities
  • docs/design/hir.md - HIR node definitions, desugaring examples, AST→HIR lowering

Compilation Pipeline

Source → Lexer → Parser → AST → Type Check → HIR → Interpreter

Key improvement: type checking completes before HIR generation, eliminating runtime type resolution overhead and enabling HIR-level optimizations (constant folding, DCE, inlining).

Original prompt

このプロジェクトはCbリポジトリのリニューアルです。
Cb言語ではHIRなどが考慮された設計ではなかったので、設計レベルで作り直します。
リポジトリの読み方はシーマイナーです

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