feat: unified type system #4

Summary

Consolidate lambda-discipline's two separate type systems into a single unified system to eliminate code duplication and enable end-to-end type information flow.

Problem

The project maintains two parallel type systems:

• Compile-time: lbd::type::Type (parsing, type checking)
• Runtime: lbd::runtime::type::Type (execution, dynamic checks)

This causes:

• Code duplication (same concepts implemented twice)
• Type information loss at compilation→execution boundary
• Maintenance burden
• Blocks static type checking implementation

Proposal

Create a single lbd::types::Type system that serves both compile-time and runtime needs, with:

• Unified TypeKind enum covering all type variants
• Factory methods for type construction
• Proper lazy evaluation support
• Comprehensive test coverage

Acceptance Criteria

• Single Type class replaces both old systems
• All integration tests pass
• Lazy evaluation properly supported
• No type information loss in pipeline
• At least 20+ integration tests demonstrating functionality

Related

Enables future work on static type checking and gradual typing.