remove enum support, reject with compile error

[cs01]

Summary

• Enums now produce a clear compile error suggesting as const objects instead
• Removes a major source of codegen complexity (string enum params, type mapping, struct layout issues)
• Converted compiler's own 3 internal enums (SymbolKind, VarKind, LogLevel) to plain const numbers

Test plan

• Existing enum test fixtures converted to @test-compile-error tests
• All 692 tests pass
• Self-hosting Stage 0 + Stage 1 pass (verify:quick)
• Error message suggests as const alternative with helpful notes

🤖 Generated with Claude Code